







CHEMISTRY and 
METALLURGY 

APPLIED TO DENTISTRY 


















By 

Vernon 3. l>all,Pb.D. 

professor of Chemistry and Directs 
or of the Chemical laboratories 
in the Dental School and in the 
Woman's IHedical School of Rorth= 
western tfniuersitp. 


















Published THE TECHNICAL PRESS 
2 by AT EVANSTON, ILLINOISU 
• MDCCCXCVIII 














29617 



COPYRIGHT, 1898, 

BY 
VERNON J. HALL. 



TWO COP* ci HSCCIVEQ, 







PREFACE. 



This book is not offered to the dental student as 
an exhaustive treatise on chemistry and metallurgy, 
but rather as an outline of information which it is 
hoped will give him a practical knowledge of those 
facts having an unquestionably important bearing 
upon dentistry. 

In writing this book the author has tried to adhere 
to three intentions : First, to adapt the course to 
the time commonly allotted to the study of these sub- 
jects; second, to reduce it to a laboratory training, 
Supplemented by the necessary amount of text work; 
and finally, to eliminate those things which are irrele- 
vant and are not likely to be taught in a practical 
course. The absence of the smatterings of organic, of 
physiological and of pharmaceutical chemistry which 
are so often given in text-books of medical and dental 
chemistry is a conspicuous feature of this book. 
The author firmly believes that* until the time given 
to the study of chemistry is increased it is unwise to 
venture into the field of organic chemistry, and that 
the time is better spent upon practical problems 
along inorganic lines, particularly as inorganic chem- 
istry has the wider application in dentistry. 



It is assumed, of course, that the student has 
received instruction either by fully illustrated lectures 
or by laboratory work, accompanied by lectures 
in the elementary principles of chemistry, and that he 
is familiar with ordinary chemical apparatus and 
with laboratory manipulation. He is then prepared 
to enter into the course of study outlined in this book. 

The author lays little claim to originality except 
in the general arrangement of the course, in the 
designing of certain pieces of apparatus, and in the 
working out of some methods in Part II. He has 
freely consulted standard books of chemistry and 
mechanical dentistry, and takes this occasion to 
acknowledge his indebtedness to the same. He also 
wishes to thank his assistants, Mr. Wilbur W. Graff 
and Mr. James E. Remington, for aid in reading proof 
and in working out details. Finally, he desires to 
express his sense of obligation to his colleague, Mr. 
George H. Ellis, and to his former instructor, Profes- 
sor Abram Van Eps Young, for valuable criticisms and 
suggestions. V. J. H. 

Evanston, III., 1899. 



CONTENTS 



Part I. 

THE METALS. DESCRIPTIVE DETAILS. 

QUALITATIVE CHEMICAL 

ANALYSIS. 



CHAPTER I. 

THE METALS. GENERAL CONSIDERATION. 

OCCUR] OF THE IfE i ai.s ... L > 

EXTRACTION OF THE METALS PROM THEIR ORES - 3 

PHYSICAL PROPERTIES OF THE METALS - - 4 

CHEMICAL PROPERTIES OF THE METALS - - 16 

CHAPTER II. 

DESCRIPTIVE DETAILS. 

SYMBOLSj COMBINING WRIGHTS; SPECIFIC GRAVI- 
IIF.S; MELTING POINTS; IMPORTANT COM- 
POUNDS; SOLUBILITIES; ALLOYS; CHIEF ORES; 
BLOWPIPE TESTS; CONFIRMATORY REACTIONS 17 

CHAPTER III. 

QUALITATIVE CHEMICAL ANALYSIS. 

GROUPING OF THE METALS 62 



x CONTENTS. , 

CHAPTER IV. 

ANALYSIS OF GROUP I. 

SEPARATION OF LEAD, SILVER AND MERCURY - 64 

CHAPTER V. 

ANALYSIS OF GROUP II. 

SEPARATION OF ARSENIC, ANTIMONY, TIN, BISMUTH, 

COPPER, CADMIUM, MERCURY AND LEAD - 66 

CHAPTER VI. 

ANALYSIS OF GROUP III. 

SEPARATION OF ZINC, ALUMINUM, IRON, MANGA- 
NESE, CHROMIUM, NICKEL AND COBALT *70 

CHAPTER VII. 

ANALYSIS OF GROUP IV. 

SEPARATION OF BARIUM, STRONTIUM AND CALCIUM - 73 

CHAPTER VIII. 

ANALYSIS OF GROUP V. 

TESTING FOR MAGNESIUM, SODIUM, POTASSIUM AND 

AMMONIUM ------ 75 

CHAPTER IX. 

TREATMENT OF METALS AND ALLOYS. 

TABLES FOR QUALITATIVE CHEMICAL ANALYSIS - 80 



CONTENTS. xi 

Part II. 

CHEMICAL TECHNOLOGY APPLIED * 
TO DENTISTRY. 



CHAPTER X. 

ALLOYS. GENERAL CONSIDERATION. 

PHYSICAL PROPERTIES OF ALLOYS 91 

CHEMICAL PROPERTIES OF ALLOYS - 94 

PREPARATION OF ALLOYS ----- 95 

CHAPTER XL 
APPARATUS 
BALANCES AND WEIGHTS; FURNACES AND ACCESSO- 
RIES; MISCELLANEOUS APPARATUS; APPARATUS 
FOR TESTING AMALGAMS; MEASURING APPA- 
RATUS; URINE ANALYSIS APPARATUS . - 97 

CHAPTER XII. 

REFINING GOLD, SILVER AND MERCURY. 

TREATMENT OF CLEAN AND MIXED SCRAP GOLD AND 
OF SWEEPINGS; TREATMENT OF "STANDARD" 
SCRAP SILVER AND OF WASTE DENTAL AMAL- 
GAM; REMOVING MECHANICAL AND METALLIC 
IMPURITIES FROM MERCURY - - - 123 

CHAPTER XIII. 

DENTAL AMALGAMS AND AMALGAM-ALLOYS. 

PROPERTIES OF AMALGAMS - 135 

PREPARING AND TESTING AMALGAM- ALLOYS AND 

AMALGAMS --..-- 141 



xii CONTENTS, 

CHAPTER XIV. 

THE ASSAY OF AMALGAM-ALLOYS. 

ESTIMATION OF TIN, COPPER AND ZINC; FIRE ASSAY 

FOR GOLD AND SILVER - - - 156 

CHAPTER XV. 

SOLDERS AND SOLDERING. 

PREPARATION OF SOLDERS 168 

CHAPTER XVI. 

MISCELLANEOUS ALLOYS. 

FUSIBLE ALLOYS; ALLOYS FOR DIES AND COUNTER- 
DIES; GOLD PLATE; TABLE OF ALLOYS - 180 

CHAPTER XVII. 

DENTAL CEMENTS. 

OXYPHOSPHATE, OXYCHLORIDE AND OXYSULPHATE - 189 
PREPARING AND TESTING CEMENTS ... 191 

CHAPTER XVIII. 

SPECIAL PROBLEMS. 

THE ANALYSIS OF TEETH, URINE AND SALIVA " - 198 



APPENDIX. 



SECTION I. WEIGHTS AND MEASURES; RULES; 

SOLUTIONS 220 

SECTION II. FORMS FOR STUDENTS' REPORT 

sheets; tables, etc. .... 227 



Part I. 



The Metals. Descriptive Details. Quali= 
tative Chemical Analysis. 



::-L-_r7Z?. : 



THE METALS- GENERAL. G0N9DGB " 




7-rr: 



2 CHEMISTRY AND METALLURGY 

long been a matter of dispute, owing to the fact that 
it has a high metallic luster and looks much like a 
metal and yet is endowed with certain chemical 
properties which closely ally it to the nonmetallic 
elements. It is now generally recognized that in this 
classification of the simple substances the chemical 
characteristics are of paramount importance; and, as 
a rule, if an element is base-forming it will be classed 
as a metal and if acid-forming as a nonmetal, without 
regard to its physical properties. 

The metals are far greater in number, and, from 
an industrial point of view, of more importance than 
the nonmetals, as they permit of a more extensive 
application in the arts. Technically speaking, the 
more important metals are gold, silver, iron, copper, 
tin, lead, mercury, platinum, zinc, antimony, nickel, 
aluminum, bismuth and magnesium. Gold, silver, 
platinum and mercury are popularly called noble 
metals and the rest are termed base. This classifica- 
tion, which had its origin in the alchemistic age, 
distinguishes those metals having a feeble affinity for 
oxygen from those which combine with this element 
with comparative ease at ordinary temperature or 
on the application of heat. With the exception of 
the last seven, the metals given in the list above have 
been known and used from the remotest time, 

Occurrence of the Metals. 

The question naturally suggests itself, where and 
in what form are the metals found? 

Many metals are very irregularly distributed and, 



APPLIED TO DENTISTRY. 3 

as already stated, are found in minute quantities 
only. Fortunately, however, those metals considered 
of most importance and utility, while constituting but 
a relatively small portion of the components of the 
earth's crust, are not diffused in minute quantities, 
but collected in beds or veins. In these veins the 
metals are found as minerals, either in the free state 
or in combination with other elements in chemical 
proportions. There are usually several minerals 
from which a metal can be extracted in profitable 
quantities, and these are called ores. The most 
abundant ores are the oxides, sulphides and car- 
bonates, examples of which are the two important 
ores of iron, the oxides, Fe 2 O s and Fe 3 4 , and the 
ores of zinc, the sulphide, ZnS, and carbonate, 
ZnC0 3 . 

Extraction of the Metals From Their Ores. 

The various mechanical and chemical methods 
employed in extracting metals from their ores consti- 
tute the art of metallurgy. The extraction of metals 
from oxide ore, as Fe 2 3 , is accomplished by 
heating at a very high temperature with carbon. As 
shown in the following equation, the carbon unites 
with the oxygen, forming carbon dioxide which passes 
off and metallic iron remains : 

2Fe 2 3 +3C = 4Fe + 3C0 2 . 
A method not practicable on a large scale but 
often employed in the laboratory is to pass hydrogen 
over the heated substance or in some manner to bring 
hydrogen in close contact with it: 



4 CHEMISTRY AND METALLURGY 

CuO+H 3 = Cu+H 2 0. 

When the ores are sulphides or carbonates they 
must be converted into oxides before they can be 
treated as shown above. 

Lastly, a method sometimes used when the metal 
exists in the free state consists in amalgamating it 
with mercury and subsequently removing the latter 
by pressure and distillation. This process is more 
often used in reducing gold and silver ores, and is 
technically known as the amalgamation process. 

Physical Properties of the Metals. 

As a class the metals are characterized by a metal- 
lic luster and by a high degree of opacity except in 
the case of gold in the form of thin sheets. With 
the exception of mercury, they are solid at ordinary 
temperature, but can be melted and in some cases dis- 
tilled by the application of heat. Many possess a 
high specific gravity, great hardness, tenacity, duc- 
tility and malleability. Some are so ductile that they 
can be drawn into very fine wire and so malleable 
that they can be hammered into sheets of great tenu- 
ity. Compared with the nonmetallic elements they 
are good conductors of heat and electricity. The 
physical properties just cited are not shown equally 
by all metals; in some instances one or more of them 
will be found deficient or entirely wanting. 

COLOR, LUSTER AND OPACITY. 

Most metals are described as white or gray in 
color, but striking exceptions are gold and copper. 



APPLIED TO DENTISTRY. 5 

Under certain conditions the color and luster of 
metals are greatly modified. This modification usually 
occurs after oxidation or after tarnishing by certain 
gases, a new substance being formed on the surface 
of the metal. Thus steel in being tempered assumes 
many brilliant colors, and copper when heated slightly 
exhibits all the colors of the rainbow. The bright 
surface of lead soon changes to a dull blue in the air 
and the brilliant luster of silver and many other 
metals is not long retained in an atmosphere of hydro- 
gen sulphide gas. The alloying of a metal with even 
small quantities of another often affects the color. 
An example of this is found in the alloying of gold 
with silver or copper. Again, metals in a finely divided 
state are often devoid of luster and possess a color 
not shown by them when in a dense mass. Precipi- 
tated gold is brown and possesses no luster at all; 
when fused, however, into a mass, it immediately 
assumes its normal color and luster. 

Metals are described as opaque. Gold, how- 
ever, in very thin sheets transmits a green or purple 
light. 

ODOR AND TASTE. 

Although these properties are not very pronounced, 
a few metals when rubbed or heated give off a pecu- 
liar odor and under certain conditions are described 
as having a "metallic" taste. Arsenic when heated 
gives off the odor of garlic. 

SPECIFIC GRAVITY. 

In specific gravity, their weight relative to water, 
the metals vary greatly. Some are heavy, as gold 



6 CHEMISTRY AATD METALLURGY 

and lead, while others are so light that they float 
on water, as potassium and sodium. They vary 
from 0.59, the specific gravity of lithium, to 22.0, that 
of osmium. Generally speaking the lighter metals 
are the more active chemically. A variation in 
specific gravity from the theoretical mean of the 
constituents is often noted in alloys. 

FUSIBILITY, VOLATILITY AND CRYSTALLINE FORM. 

The most readily fusible metal is mercury. Its 
melting point, in reality its freezing point, is about 
—39° C. 

The alkali metals, potassium and sodium, melt at 
the temperature of boiling water; a great number melt 
at red heat and a few at white heat only. Platinum 
and some of the rarer metals associated with it in na- 
ture require the heat of the oxyhydrogen blowpipe to 
effect their fusion. The melting point of a metal is 
often greatly modified by the presence of even traces of 
other metals. Many of the so-called fusible alloys, 
composed chiefly of tin, lead and bismuth, melt at 
the temperature of boiling water. 

Some metals volatilize on being heated; arsenic 
volatilizes at red heat and can be melted only under 
pressure. Other metals which volatilize readily at 
red heat or above are cadmium, zinc, lead and mer- 
cury. The last named is slightly volatile at ordinary 
temperature. 

Upon being melted and slowly cooled many metals 
assume a definite crystalline form. This is particularly 
true of those metals melting at comparatively low 



APPLIED TO DENTISTRY. 7 

temperatures, as bismuth and antimony. Under vari- 
ous other conditions metals show a tendency to crys- 
tallize; zinc and arsenic can be crystallized by subli- 
mation; silver has been crystallized from its solutions 
by galvanic action and at times has been made to 
assume a crystalline form while in the solid state by 
repeated heating and cooling and by percussion or 
other forms of mechanical working. Metals occurring 
free in nature usually are crystallized. 

MALLEABILITY AND DUCTILITY. 

Some metals are capable of being rolled, ham- 
mered, drawn, or otherwise modified in form by vari- 
ous mechanical means, without becoming disrupted. 
This property is expressed by the terms malleability 
and ductility. Gold is recognized as the most mal- 
leable and at the same time the most ductile metal 
known. It can be rolled or hammered into sheets 
less than suainn) °f an i ncn in thickness, and drawn 
into wire so fine that one mile will weigh less than 
one gram. Malleability and ductility are by no means 
proportional in the same metal. Iron, although infe- 
rior to tin in malleability, is much more ductile, and 
can be drawn into very fine wire. In many metals 
malleability and ductility are wanting altogether. 
This is exemplified in the cases of bismuth, antimony 
and other metals more or less crystalline in structure. 
Both malleability and ductility are influenced by 
temperature, by mechanical working and by the 
presence of traces of other metals. As a rule, 
these properties are increased by an increase of tem- 
perature, and if diminished in working the metal, 



8 CHEMISTRY AND METALLURGY 

they can be restored by heating and cooling slowly or 
quickly, usually the former. This is known as 
annealing. The effects of impurities upon a metal 
are shown in the case of gold. The presence of 
minute traces of lead, bismuth or antimony in gold 
greatly impairs its malleability and correspondingly 
modifies its ductility. 

In the following tables the metals are arranged in 
the order of their malleability and ductility: 

TABLE OF MALLEABILITY. TABLE OF DUCTILITY. 

Most malleable. Most ductile. 

1. Gold. 7. Lead. 1. Gold. 7. Cadmium. 

2. Silver. 8. Cadmium. 2. Silver. 8. Aluminum. 

3. Aluminum. 9. Zinc. 3. Platinum. 9. Zinc. 

4. Tin. 10. Iron. 4. Iron. 10. Tin. 

5. Copper 11. Nickel. 5. Nickel. 11. Lead. 

6. Platinum. Least malleable. 6. Copper. Least ductile. 

HARDNESS, ELASTICITY AND TENACITY. 

The metals differ greatly in hardness. Potassium 
and sodium are plastic. Tin and lead are so soft 
that they can be scratched with the finger nail, while 
steel can be made so hard that it will scratch glass. 
The hardening of a metal is usually accomplished by 
adding to it small quantities of various substances. 
The presence of one to one and one-half per cent of 
carbon in steel renders it suitable for making tools, 
while the addition of even smaller quantities of chro- 
mium is said to harden it and improve its quality. 
Gold and silver in the pure state are too soft for general 
use; upon alloying them with copper they become quite 
hard and much more serviceable for coin and for 
other articles. 



APPLIED TO DENTISTRY, 9 

In the following table a comparison of the hard- 
ness of the principal metals is made with lead, the 

softest metal in common use. 
i 

TABLE OF HARDNESS. 

Softest. 

Lead 1.0 Antimony 1.8 

Tin 1.2 Zinc 1.9 

Cadmium 1.4 Platinum 2.0 

Aluminum 1.5 Copper 2.4 

Bismuth l.G Iron 2.4 

Gold 1.7 Nickel 2.5 

Silver 1.8 Hardest. 

In elasticity, or the power of recovering original 
dimensions after being bent, twisted, stretched, etc., 
the metals are quite deficient. In many cases, how- 
ever, this property can be induced by alloying, ham- 
mering, tempering, etc. When gold is alloyed with a 
small proportion of platinum it becomes very elastic. 
When iron is converted into steel and then tempered 
in a certain manner, it becomes adapted to various 
uses in which great elasticity is required, as in making 
sword blades and watch springs. 

Closely connected with hardness and elasticity and 
with malleability and ductility is tenacity, the power 
possessed by metals of resisting forces which tend to 
separate their particles by tension or crushing. Wide 
differences are observed in the tenacity of the met- 
als. Lead is the lowest of those recognized as possess- 
ing this property, while iron is one of the most tena- 
cious metals known. Some metals show but a slight 
degree of tenacity and are said to be brittle; for ex- 
ample, antimony, arsenic and zinc. Tenacity is influ- 



10 CHEMISTRY AATD METALLURGY 

encedby temperature, by the mechanical working of 
the metal and by its purity. As a rule an increase of 
temperature beyond certain limits reduces the tenacity. 
Iron and gold heated to 100° C. are somewhat increased 
in tenacity, but beyond that point a decided de- 
crease is noted. It is a peculiar fact that, when gold, 
silver, iron and certain other metals are heated to a red 
heat and cooled slowly the tenacity of each is greatly 
diminished. This undoubtedly is due in part at least 
to a rearrangement of the molecules. Silver, for ex- 
ample, ordinarily very tough, can be made to 
assume a granular form and to become brittle by re- 
peated heating and cooling. The alloying of metals 
often reduces the tenacity, but more often increases 
it; and the mechanical working of a metal can be 
made to increase or decrease the tenacity in propor- 
tion as it induces a fibrous or crystalline texture. As 
a rule the more fibrous metals exhibit a high degree 
of tenacity, while those crystalline in structure are 
deficient in that respect. It is obvious that the 
properties, hardness, elasticity, malleability, ductil- 
ity and tenacity are more or less intimately connected, 
and anything affecting one may affect all to a certain 
extent. 

In the following table the metals are arranged in 
the order of their tenacity, cobalt being the strongest 
and lead the weakest of the metals: 



Most tenacious. 






1. Cobalt. 


4. Copper. 


7. Gold. 10. Cadmium. 


2. Nickel. 


5. Platinum. 


8. Aluminum. 11. Tin. 


3. Iron. 


6. Silver. 


9. Zinc. 12. Lead. 

Least tenacious. 



APPLIED TO DENTISTRY. 11 

CHANGE OF VOLUME WITH TEMPERATURE AND SOLIDIFI- 
CATION. 

Metals expand when heated and, as a rule, a given 
metal expands uniformly, within certain limits, for 
equal increments of temperature. As the force ex- 
erted in expansion is very great, it is highly important 
in the industrial arts that the exact amount of expan- 
sion which different metals undergo within certain 
limits of temperature be known and that provision 
be made for this change of dimension. Thus in 
building railways, bridges and buildings, the expan- 
sion of the steel in warm weather is always taken into 
consideration. In the table given below the fraction 
indicates the increase in length, i. e., so-called linear 
expansion of a rod of the given metal by a rise of 
temperature from 0° to 100° C. As most metals 
expand equally in all dimensions, the cubic expansion 
can be calculated by multiplying the linear expansion 
by three. 

Greatest expansion. 

Cadmium fa Copper fa 

Lead yjj Bismuth -${ 

Zinc fa Gold 

Aluminum ±1^ Nickel y J- 7 

Tin fa Iron (cast) fa 

silver fa Antimcny fa 

Platinum ttts 

Least expansion. 

When metals pass from the liquid to the solid 
state they suffer a change of volume, which in most 
cases is contraction. Among the common metals 
which contract are silver, zinc, lead, aluminum, cop- 



7TT7 
68^ 



12 CHEMISTRY AND METALLURGY 

per and tin. Examples of metals which expand are 
bismuth and antimony. In employing metals for 
various purposes in the arts, particularly in making 
castings of any sort in which perfect detail is required, 
it is very essential that this tendency to decrease in 
volume be counteracted. Often this can be accom- 
plished by alloying with other metals, especially with 
those which expand on solidification. An alloy com- 
posed of four parts of lead, one part of tin and one 
part of antimony furnishes extremely sharp castings, 
and is employed in the manufacture of type and in 
the production of dies for swaging purposes. 

SPECIFIC HEAT AND CONDUCTING POWER. 

The specific heat of a substance represents its 
capacity for heat or, more accurately defined, it rep- 
resents the quantity of heat required to raise the 
temperature of a certain weight of a substance a 
certain number of degrees as compared with that re- 
quired to raise the temperature of an equal weight 
of water the same number of degrees. Thus it 
takes but ^ as much heat to raise the temperature 
of a pound of mercury ten degrees as it does to raise 
a pound of water the same number of degrees. 
Water being taken as the standard, mercury then has 
a specific heat of ^ or 0.0333. The capacity of the 
alkali metals for heat is very great as, in the case of 
sodium, over five times greater than that of silver 
and nearly ten times that of gold. 

The following table gives the specific heats of the 
common metals : 



APPLIED TO DENTISTRY. 



13 



Sodium 0.2934 

Aluminum 0.2143 

Potassium 0.1696 

Iron 0.1123 

Nickel 0.1086 

Cobalt 0.1070 

Zinc 0.0955 

Copper 0.0952 



Cadmium 0.0567 

Tin 0.0562 

Antimony 0.0508 

Mercury 0.0333 

Gold 0.0324 

Lead 0.0314 

Platinum 0.0311 

Bismuth 0.0308 



Silver 0.0570 

The metals are the best known conductors of heat 
and electricity. In conductivity silver exceeds all 
other metals and is taken as a standard of comparison. 
Generally speaking, the best conductors of heat are at 
the same time the best conductors of electricity. 
According to Matthiessen, alloying or increasing the 
temperature of a metal diminishes its power of con- 
ducting electricity. 

The following tables show the relative conduc- 
tivity of the more important metals, taking silver as 
100 at 0° C. 



FOR HEAT. 

Silver 100.0 

Copper 85.5 

Gold 53.2 

Aluminum 31.3 

Zinc 28.1 

Cadmium 20.1 

Tin 15.5 

Mercury (liquid) 13.5 

Iron 11.9 

Nickel 

Lead 8.5 

Platinum 8.4 

Antimony 4.0 

Bismuth 1.8 



FOR ELECTRICITY. 

Silver.... 100.0 

Copper 97.8 

Gold 76.7 

Aluminum 65.5 

Zinc 29.6 

Cadmium 24.4 

Iron 14.6 

Platinum 14.5 

Tin 14.4 

Nickel 12.9 

Lead 8.4 

Antimony 3.6 

Mercury 1.8 

Bismuth 1.4 



14 CHEMISTRY AND METALLURGY 

MAGNETIC, GALVANIC AND THERMO-ELECTRIC 
PROPERTIES. 

Metals affected by the magnet are said to possess 
magnetic quality, and are divided into two classes, 
paramagnetic and diamagnetic, according as they 
are attracted by the magnet or repelled by it.* To 
the former class belong iron, nickel, cobalt, manga- 
nese and chromium. Representatives of the latter 
class are arsenic, gold, copper, silver, lead, mercury, 
cadmium, tin, zinc, antimony and bismuth. 

Magnetism is communicable; thus a bar of soft 
iron when brought near a magnet immediately be- 
comes magnetic and retains this property while under 
the influence of the magnet. Steel acquires mag- 
netism slowly and retains it permanently, forming the 
so-called permanent magnet. Magnetism is destroyed 
at red heat, except in the case of cobalt, which, to a 
slight degree, retains its magnetism until white heat 
is reached. A natural magnetic substance is the ore 
of iron known as the magnetic oxide, Fe 3 4 , and com- 
monly called lodestone. 

When two dissimilar metals in contact with each 
other are immersed in any conducting liquid which 
acts upon either of them a current of electricity is 
produced. Thus when a zinc plate and a platinum 
plate are placed in sulphuric acid and then connected 
outside the acid in any manner, as by a copper wire, 

*A more accurate distinction is: A paramagnetic metal is one 
which tends to arrange itself parallel to the lines of force about the 
magnet, and a diamagnetic metal is one which tends to set itself at 
right angles to these lines, 



APPLIED TO DENTISTRY. 15 

chemical action takes place, the result being that the 
zinc is dissolved, that hydrogen is evolved at the 
platinum plate and that a current of electricity passes 
through the circuit. This phenomenon is known as 
galvanic action, and the system composed of zinc, 
platinum and acid arranged as indicated constitutes a 
galvanic, or more properly a voltaic cell, and 
embodies the principles upon which common electric 
batteries are constructed. Of the two metals in the 
cell, the one attacked by the liquid is called the positive 
metal or plate and the other the negative metal 
or plate. In the liquid the current of electricity flows 
from the positive to the negative metal, while in the 
connecting wire it flows from the negative to the 
positive metal. 

Galvanic action has an important effect upon 
certain metals employed for various purposes in the 
mouth, and will be more fully referred to later. 

When two dissimilar metals are connected at two 
junctions and one of these junctions is heated a cur- 
rent of electricity results. Electricity thus induced 
by heat is commonly called thermo-electricity, and a 
pair of conductors joined as indicated constitute a 
thermo-couple. The strength of a thermo-electric 
current, although in no case very great, is proportional 
to the difference in temperature between the two 
junctions, and its direction is dependent upon the 
metals constituting the thermo-couple. Generally 
speaking, those metals which possess a decided 
crystalline structure produce the strongest current; 
for example, bismuth and antimony. 



16 CHEMISTRY AND METALLURGY 

Chemical Properties of the Metals. 

Most metals unite with one another to form alloys 
and with mercury to form amalgams. The chemistry 
of these substances is not very well understood 
except in cases in which metallic crystals of definite 
composition are formed. In addition to the com- 
pounds just mentioned the metals combine with the 
nonmetallic elements as follows : With chlorine to 
form chlorides, with bromine to form bromides, with 
iodine to form iodides, with sulphur to form sulphides, 
with oxygen to form oxides, with oxygen and 
hydrogen to form hydroxides, and with numerous 
other elements to form compounds of importance. 

Metallic oxides and hydroxides, commonly known 
as bases, unite with acids and form a class of com- 
pounds, usually neutral, called salts. Another chemical 
characteristic of the metals is their power of replacing 
hydrogen in acids, the final products again being 
salts. Examples of common salts are the chlorides, 
the nitrates, the sulphates, the carbonates, the 
acetates, etc. 



APPLIED TO DENTISTRY. 17 



CHAPTER II 



DESCRIPTIVE DETAILS. 

LEAD. Symbol, Pb. Combining weight, 206.95. 
Specific gravity, 11.38. Melting point, 326.2° C. 
Lead can be easily rolled into sheets, but cannot be 
drawn into wire. It is very soft, not at all elastic, apoor 
conductor of heat and electricity, and ranks the low- 
est in tenacity. It is quite volatile at red heat. When 
remelted several times it becomes brittle, due to the 
presence of traces of dissolved oxide. In this condi- 
tion the metal can be toughened by melting under 
powdered charcoal. Lead tarnishes in the air, lead 
monoxide, Pb 2 0, being formed. In an atmosphere of 
hydrogen sulphide gas lead becomes coated with a film 
of lead sulphide, PbS. It forms four oxides, the most 
important of which are litharge, PbO, and red lead, 
Pb 3 4 . Many lead compounds, particularly white 
lead, 2PbCO v Pb(OH) 2 , are used as pigments. Me- 
tallic lead is somewhat soluble in impure water, and 
quite soluble in hot water. It is insoluble in hydro- 
chloric and sulphuric acids, but readily soluble in 
nitric and acetic acids, lead nitrate, Pb(N0 3 ) 2 , and 
lead acetate, Pb(C 2 H 3 2 ) 2 , being formed. 

Alloys.* Soft solders, type metal, pewter and 
fusible alloys. Lead amalgamates readily. 

*For the composition of the various alloys referred to in this 
chapter, see chapters on alloys, Part II. 



18 CHEMISTR Y AND ME TALL URGY 

Chief Ore. Galena, PbS. Reduced by roasting 
until considerable lead oxide and lead sulphate are 
formed. This mixture is then heated, air being 
excluded, and the following reactions take place : 

PbS0 4 + PbS = 2Pb+2S0 8 
2PbO+PbS = 3Pb+S0 3 . 

Another method consists in simply heating the ore 
with iron. 

PbS+Fe = Pb+FeS. 

Blowpipe Tests. On charcoal before the blowpipe 
flame metallic lead gives an easily fusible, soft, gray 
bead, and an incrustation of oxide, PbO, lemon yellow 
while hot, sulphur yellow when cold, surrounded by 
a white border of lead carbonate. Compounds of 
lead, such as lead chloride or sulphate, are reduced 
to metallic lead on charcoal by fusing with sodium 
carbonate. 

Confirmatory Reactions. Dissolve the bead of lead 
in dilute nitric acid.* This solution gives, upon 
adding hydrochloric acid, a white precipitate of lead 
chloride, PbCl 3 , dissolved, after filtering, by pour- 
ing hot water over it on the filter paper. Add sul- 
phuric acid to this water solution. A fine white pre- 
cipitate of lead sulphate, PbS0 4 , is formed. Filter, 
and reduce this precipitate to metallic lead by fusing 
on charcoal with sodium carbonate. 

*In dissolving metals, use as little acid as possible and apply 
heat to promote the reaction. When dissolved, dilute with con- 
siderable water or, better still, evaporate nearly to dryness in a 
porcelain dish and take up the residue with water before apply- 
ing tests. 



APPLIED TO DENTISTRY. 19 

SILVER. Symbol, Ag. Combining weight, 107.92. 
Specific gravity, 10.55: Melting point, 954° C. In 
degree of malleability and ductility silver is next to 
gold, and as a conductor of heat and electricity it 
surpasses all other metals. It is somewhat harder 
and more tenacious than gold, but still too soft for 
general use. Silver is hardened by alloying and ham- 
mering. It is a pure white metal, not changed by 
air or water, but readily tarnished by sulphur or its 
compounds, silver sulphide, Ag 2 S, being formed. 
Silver absorbs about twenty volumes of oxygen when 
melted and contracts upon cooling, evolving the 
included oxygen. If the cooling is sudden the oxygen 
in escaping causes the metal to spirt. This is com- 
monly called the « spitting" or " sprouting " of 
silver. Silver has few compounds of commercial 
importance except the nitrate, AgN0 3 , used in 
medicine, and the chloride, bromide and iodide, 
AgCl, AgBr, Agl, all useful in photography. Silver 
is practically insoluble in hydrochloric acid and in aqua 
regia, slowly soluble in sulphuric, but readily soluble 
in nitric acid, silver nitrate, AgN0 3 , being formed. 

Alloys. Coin, jewelry, silver solders and amalgam- 
alloys, i. e., alloys which when amalgamated are 
employed in filling cavities in teeth. Silver amal- 
gamates slowly, and the union is attended in most 
cases with an increase of volume. In certain cases, 
at least, silver amalgams possess definite chemical 
composition. Native amalgams of silver frequently 
are found which are true chemical compounds. 



20 CUE MIS TR Y AND ME TALL UR G Y 

Chief Ores. Argentite, Ag 2 S. Silver is often found 
in paying quantities in galena. 

Various methods are employed in treating silver 
ores. When silver is extracted from galena the Pat- 
tison method is used. After both lead and silver are 
reduced to the metallic state, the silver is concentrated 
by fusing and allowing the lead to crystallize; metal- 
lic lead free from silver separates. When an alloy rich 
in silver is obtained, the remaining lead is separated 
by the operation of cupellation, in which the mixture 
is heated in bone ash vessels in contact with air; the 
lead oxidizes and the litharge formed is partly driven 
off and partly absorbed by the bone ash, leaving the 
silver in the metallic state. 

Another method of extracting silver from its ores 
is the amalgamation process. The ore is roasted with 
common salt, by which means silver chloride is 
formed. The mixture is placed in casks and treated 
with iron and water. 

2AgCl+Fe = 2Ag+FeCl 2 . 

As observed, the iron reduces the silver chloride 
to metallic silver. Mercury is next added. This forms 
with the silver an amalgam, which can be sepa- 
rated from the rest of the mixture. When this amal- 
gam is heated in an iron retort the mercury distills 
over, leaving the impure silver. Pure silver may be 
obtained by dissolving the impure varieties in nitric 
acid and adding common salt.* The resulting silver 
chloride, after being washed, can be reduced to 
metallic silver by fusing with sodium carbonate. 
2AgCl + Na 2 C0 3 =2Ag + C0 2 + 0+2NaCl. 

*See Chapter XII. 



APPLIED TO DENTISTRY. 21 

Blowpipe Tests. On charcoal silver fuses easily, 
giving a white, clear bead, accompanied by no 
incrustation of oxide, Silver chloride and other 
compounds of silver are reduced to metallic silver 
by fusing on charcoal with sodium carbonate. 

Confin?iatory Reactions. Dissolve the bead in nitric 
acid and then dilute with water. This solution gives 
with hydrochloric acid a white, curdy precipitate of 
silver chloride, AgCl, insoluble in hot water (distinc- 
tion from lead chloride) but soluble on the filter 
paper, in hot ammonium hydroxide. If nitric acid is 
added to this ammoniacal solution the precipitate 
of silver chloride reappears. Filter and* reduce 
to metallic silver by fusing on charcoal with sodium 
carbonate. 

MERCURY. Symbol, Hg. Combining weight, 
200. Specific gravity, 13.59. Melting point (freez- 
ing), —38.8° C. Boiling pokit, 357.2° C. Mercury, 
also known as quicksilver, is the only metal liquid at 
ordinary temperature. When pure it has a brilliant 
silver color, but a slight trace of impurity is shown by 
the formation of a scum on its surface. It does not 
oxidize, but slowly volatilizes in the air at ordinary 
temperature. One of the peculiarities of mercury is 
its tendency to unite with other metals and make the 
class of substances known as amalgams. Mercury 
forms two oxides, mercurous oxide, Hg 2 0, and mer- 
curic oxide, HgO. The latter is commonly called red 
precipitate. In addition to these compounds mercury 
forms others of importance, particularly the chlorides, 



22 CHEMISTR V AND ME TALL URGY 

Hg 2 Cl 2 , commonly called calomel, and HgCl 3 , known 
as corrosive sublimate, a powerful disinfectant. Mer- 
curic sulphide, HgS, often called vermilion or cinna- 
bar, is employed in coloring rubber. When used in 
coloring vulcanizable rubber for artificial dentures, 
vermilion free from metallic mercury, red lead, etc., 
with which it is sometimes contaminated, should be 
employed. Mercury is insoluble in hydrochloric 
and sulphuric acids but soluble in aqua regia, 
forming mercuric chloride, HgCl 2 , and in nitric acid, 
forming mercurous and mercuric nitrates, HgN0 3 
andHg(N0 3 ) 2 . 

Alloys. Under certain conditions mercury unites 
with nearly all metals to form amalgams, some of 
which, however, are very unstable substances. Mer- 
cury when mixed with certain alloys, composed 
chiefly of silver and tin, forms an amalgam widely 
used in filling cavities \n teeth. 

Chief Ore. Cinnabar, HgS. Reduced by roasting 
in the air and then refined by distilling with lime: 

HgS+0 2 = Hg+S0 2 . 

Blowpipe Tests. Metallic mercury quickly vola- 
tilizes on charcoal and gives a metallic mirror when 
heated in a glass tube sealed at one end. 

Confirmatory Reactions. 

Mercurous Compounds. Dissolve some mercury 
in very dilute nitric acid. Hydrochloric acid added 
to this solution produces a white precipitate of mer- 
curous chloride, Hg 2 Cl 2 , insoluble in hot water (dis- 



APPLIED TO DENTISTRY. 23 

tinction from lead chloride). Filter and treat on the 
filter paper with ammonium hydroxide. The precipi- 
tate blackens, but does not dissolve (distinction from 
silver chloride), a complex compound, mercurous 
ammonium chloride, NHoHg 2 Cl, being formed. 

Mercuric Compounds. Dissolve some mercuric 
nitrate or chloride in hot water. Add hydrochloric 
acid. No precipitate is formed. Add hydrogen sul- 
phide gas. In time a black precipitate of mercuric 
sulphide, HgS, is obtained. Filter, dry and heat 
with sodium carbonate in a glass tube sealed at one 
end. A deposit of metallic mercury will appear on 
the cool part of the tube. 

ARSENIC. Symbol, As. Combining weight, 75. 
Specific gravity, 4 . V 1 . Melting point (under pressure) 
between silver and antimony. Arsenic is usually 
classed as a nonmetal, although in some respects 
it resembles the metals. It is sometimes black and 
sometimes steel-gray in color. It is brittle and pul- 
verizable. It slowly oxidizes in moist air and when 
heated it volatilizes without melting. At a high tem- 
perature it burns with a bluish flame, emitting the 
odor of garlic, and becoming arsenious oxide, As 2 3 . 
Metallic arsenic is not poisonous, but the "white" 
arsenic, or arsenious oxide, is extremely so. Metallic 
arsenic is quite uncommon as a metal and is of little 
value. Arsenious oxide has many uses, particularly 
in medicine and dentistry. In the latter it is used 
as a devitalizing agent. Metallic arsenic is but slightly 
acted upon by common acids in the cold. It dissolves 



U CHEMISTR Y A ND METALLVRG Y 

in hot concentrated nitric acid and in aqua regia, 
forming arsenic acid, H 3 As0 4 . Arsenious oxide is 
nearly insoluble in cold water, but soluble in hydro- 
chloric and sulphuric acids, in alkalies and in the 
fluids of the stomach. 

Alloys. Arsenic forms no alloys of importance. 
It is present in shot to the extent of one-half percent, 
and is a very persistent impurity in zinc and tin. 

Chief Ore. Arsenical pyrites, FeAsS. Reduced 
by heating, air being excluded. 

FeAsS = As+FeS. 

Blowpipe Tests. Metallic arsenic volatilizes with- 
out fusing, giving the odor of garlic, and a white 
incrustation of arsenious oxide, As 2 O a , on the charcoal. 

Compounds, as arsenious oxide, when heated with 
charcoal in a glass tube sealed at one end, give a 
deposit of gray metallic arsenic on the cool part of 
the tube. 

Confirmatory Reactions. Dissolve some arsenious 
oxide in hydrochloric acid with the aid of heat. Dilute 
with water and add hydrogen sulphide gas. A yel- 
low precipitate of arsenious sulphide, As 2 S 3 , is 
formed. Filter. Place the precipitate and paper in 
a porcelain dish and digest with yellow ammonium 
sulphide. The precipitate dissolves. 

Marsh's Test for Arsenic. A test for arsenic more 
delicate than those given above is that known as 
Marsh's test. In making this test a modified hydro- 
gen generator (Fig. 25) commonly known as Marsh's 
apparatus is employed. The flask is charged with zinc 



APPLIED TO DEXTISTRY. 25 

and hydrochloric acid as usual in generating hydrogen. 
After the evolution of gas has continued until the air is 
expelled, a towel is wrapped about the apparatus as 
a precautionary measure, and the hydrogen is lighted 
at the small opening of the exit tube. The solution 
to be tested is poured into the generator through the 
funnel tube, and a piece of cold porcelain is held in 
contact with the flame. The compound, arsenious 
hydride, formed in the generator passes out and burns 
at the opening, depositing metallic arsenic on the 
porcelain. Arsenic spots are of a steel gray luster 
and soluble in sodium hypochlorite. 

ANTIMONY. Symbol, Sb. Combining weight, 
Specific gravity, 6.7. Melting point, 432° C. 
Antimony is a very brittle and readily pulverizable 
metal. It is bluish white in color, possesses a crys- 
talline structure and in general appearance resembles 
bismuth. It does not readily change in dry air at 
ordinary temperature, but when heated to a red heat 
it yields antimonious oxide, Sb 2 3 . Hydrogen sul- 
phide only slightly tarnishes it. There are no com- 
pounds of antimony of much importance. The metal, 
however, is widely used in alloys. In its chemical 
properties antimony resembles arsenic. It is practi- 
cally insoluble in hydrochloric and sulphuric acids 
except when the latter is concentrated and boiling. 
It is oxidized by nitric acid forming antimonic acid, 
H 3 Sb0 4 . Aqua regia dissolves it, forming antimony 
chloride, SbCl 3 . It is soluble also in tartaric acid 
but not in alkalies. 



26 CHEMISTR Y AND ME TALL URG Y 

Alloys. Britannia metal, type metal, Babbitt 
metal. Antimony hardens alloys and causes them to 
expand on cooling, thus filling the mold. It forms an 
amalgam which decomposes in air and water. 

Chief Ore. Stibnite, Sb 2 S 3 . Reduced by first 
roasting and then heating with carbon. 

Sb 2 4 +4C = 2Sb+4CO. 

Blowpipe Tests. Antimony fuses easily and covers 
the charcoal with a white incrustation of antimonious 
oxide, Sb 2 3 . If the bead is dropped from the char- 
coal onto the table it skips about, leaving a white 
trail. 

Confirmatory Reactions, Dissolve the bead in a 
little aqua regia, dilute with water, disregard any 
precipitate, and add hydrogen sulphide gas. An 
orange red precipitate of antimonious sulphide, Sb 2 S 3 , 
is formed. Dissolve, like arsenious sulphide, by boil- 
ing with yellow ammonium sulphide. 

Marsh s Test for Antimony. The Marsh test for 
antimony is conducted in the same manner as the cor- 
responding test for arsenic. Hydrogen is generated 
in the apparatus and after the air is expelled the solu- 
tion to be tested is poured in; a towel is wrapped 
about the apparatus, the gas is ignited and a piece of 
cold porcelain is held against the flame. Antimonious 
hydride is decomposed and yields a brown or black 
velvety spot of metallic antimony, insoluble in 
sodium hypochlorite. 



A J TO L "TRY. 

TIN. Symbol, Sn. Combining weight, 111 
cific g: - ng point. _ l.7 # C - a is 

a very white metal, much resembling silver in this 
respect, bat not so bright in color. It is soft and 
malleable, capable of being hammered intc thin 

foil, but not ductile or tenacious. It does not 

readily change in the air at ordinary temperature, but 
it quickly tarnishes in hydrogen sulphide gas, stan- 
nous sulphide, SnS, being formed. It burns at a 
white heat, stannic oxide, Sn suiting. When 

crushed or bent tin emits a peculiar crackling sound. 
Few compounds of tin are of importance M saic 
gold, used as a bronze powder, is tin sulphide, SnS f . 
A pure tin are Ban: a tin and block tin. T:^ 
dissolves rapidly in pure concentrated hydrochloric 
and sulphuric acids, forming stannous chloride, 
SnCL, and stannous sulphate :;c acid 

rapidly convert to a white, insoluble substance, 

metastannic acid, H 10 SrijO ls "(variable), 
regia diss 5nCl 4 . 

Alloys. am-alloys, bronze, soft solders, 

type metal, Britannia metal and fusible alloys. Tin 
amalgama he product being used in 

"silvering" mirrors. The combination of tin and 
mercury is attended by a de in volume. 

Chief Ore. d stone, Sn0 2 . The ore isroas 

to remove a: and then reduced by heating with 

coal. 

SnO : -:C = 5r.-:CO. 

Blow pipe Test. Tin fuses eas iaganincrus- 



28 CHE MIS TR Y AMD ME TALL URGY 

tation of stannic oxide, Sn0 2 , yellow while hot, white 
when cold. Tin is very oxidizable. 

Confirmatory Reactions. Dissolve the bead in hydro- 
chloric acid, dilute with water and to a portion add 
hydrogen sulphide gas. A brown precipitate of stan- 
nous sulphide, SnS, appears, soluble, like the sul- 
phides of arsenic and antimony, in hot yellow 
ammonium sulphide. To another portion add a solu- 
tion of mercuric chloride; a white precipitate of 
mercurous chloride, Hg 2 Cl 2 , appears, and this is 
taken as evidence of tin. The reaction involved is 
as follows: When mercuric chloride, HgCl 2 , a solu- 
ble substance, is added to stannous chloride, SnCl 2 , 
a reducing agent, the latter becomes oxidized to 
stannic chloride, SnCl 4 , also soluble, and the former 
is reduced to an insoluble form, mercurous chloride, 
Hg 2 Cl 2 , hence it precipitates and proves the pres- 
ence of tin in the solution. 

BISMUTH. Symbol, Bi. Combining weight, 
208.9. Specific gravity, 9.76. Melting point, 268.3° C. 
Bismuth is a very brittle metal, slightly reddish 
yellow in color. It possesses a crystalline structure 
and resembles antimony except in color. Under ordi- 
nary conditions it remains unchanged in the air but 
at a red heat it burns with a blue flame, the oxide of 
bismuth, Bi 2 O s , being formed. In the presence of 
moisture, hydrogen sulphide forms bismuth sulphide, 
Bi 2 S 3 . There are few important compounds of bis- 
muth except bismuth subnitrate, Bi(OH) 2 N0 3 , used 
in medicine. Bismuth is insoluble in hydrochloric 



APPLIED TO DENTISTRY. 29 

acid and but slightly soluble in sulphuric. It is 
very soluble in nitric acid, forming bismuth nitrate, 
Bi(N0 3 ) 3 . 

Alloys. Bismuth is chiefly used in the so-called 
fusible alloys, to which it imparts a low melting 
point. Examples of fusible alloys are Wood's, New- 
ton's and Rose's metals. Bismuth amalgamates 
readily and is sometimes used to adulterate mercury. 
One part of bismuth in eight thousand parts of 
mercury can be detected and separated as a black 
powder by shaking the mercury in a test tube or 
other suitable vessel. 

Chief Ores. Bismuth occurs native, also as bis- 
muth glance, Bi 2 S 3 , and as bismuth ocher, Bi 2 3 . 
The metal is reduced from the oxide by fusing with 
carbon. Native metallic bismuth is separated from 
the ore by heating in inclined iron retorts. The metal 
melts at a low heat, and runs from a small opening in 
the lower end of the retort. 

Blowpipe Test. On charcoal bismuth fuses 
readily, giving a brittle bead, which distinguishes it 
from lead, and an incrustation of bismuth oxide, 
Bi 2 3 , orange yellow while hot, lemon yellow when 
cold. 

Confirmatory Reactions. Dissolve the bead in nitric 
acid and dilute with water. To a portion add 
ammonium hydroxide to alkaline reaction. A white 
precipitateof bismuth hydroxide, Bi(OH) 3 , is formed. 
Filter, and pour over the precipitate on the filter 



30 CHE MIS TR Y AND ME TALL UK G Y 

paper hot stannite* The precipitate turns black. To 
the second portion add hydrogen sulphide gas. A 
black precipitate of bismuth sulphide, Bi 2 S 3 , is 
formed, insoluble in ammonium sulphide (distinction 
from arsenic, antimony and tin). Filter and digest 
with nitric acid in a porcelain dish. The precipitate 
dissolves. 



COPPER. Symbol, Cu. Combining weight, 63.6. 
Specific gravity, 8.95. Melting point, 1054° C. Spe- 
cific gravity and melting point are both variable. Cop- 
per is a red metal of brilliant luster, not readily tar- 
nished except in moist air and in hydrogen sulphide gas. 
In the former case basic carbonate, CuC0 3 .Cu0 2 H 2 , 
is formed and in the latter copper sulphide, CuS. 
Copper is quite a difficult metal to fuse. When 
heated a brilliant film of oxide covers its surface. 
Copper is one of the most malleable metals, but 
only approaches iron in ductility and tenacity. As a 
conductor of heat and electricity it is next to silver. 
Important compounds of copper are cuprous oxide, 
Cu 2 0, cupric oxide, CuO, copper sulphate, CuS0 4 , 
and copper arsenite, commonly known as Scheele's 
green, a very poisonous substance used as a pigment. 
Copper dissolves in nitric acid forming copper 
nitrate, Cu(N0 3 ) 2 , and in sulphuric, forming copper 
sulphate, CuS0 4 . 

*To make stannite add potassium hydroxide to a drop of 
stannous chloride, in a test tube, until the precipitate at first 
formed redissolves, and the liquid is strongly alkaline. 



APPLIED TO DENTISTRY. 31 

Alloys. Coin, brass, bronze, gun metal, bell metal, 
aluminum bronze, German silver, Babbitt metal, 
amalgam-alloys, and in various alloys made to imitate 
gold. It amalgamates if its surface is perfectly 
clean. The precipitated copper, obtained by the 
action of metallic iron or zinc in a weak solution 
of copper sulphate, is used in dentistry as a filling 
material when amalgamated. 

Chief Ores. Copper is found native, also as copper 
glance, Cu 2 S, and as malachite, CuC0 3 .Cu0 2 H 2 , 
Oxide and carbonate ores are reduced by smelting 
with coal. The reduction of sulphide ores is compli- 
cated owing to the difficulty with which they are 
oxidized. The ore is first roasted in the air then 
with a siliceous flux and carbon, copper matte being 
formed. This process is repeated until the ore is 
nearly pure copper sulphide and then it is reduced 
to metallic copper by heating in the air, the oxide 
formed reacting as follows : 

Cu 2 S + 2Cu„0 = 6Cu + S0 2 . 

Another important method of reducing copper is 
by electrolysis. 

Blowpipe Tests. Copper fuses with difficulty on 
charcoal before the ordinary blowpipe flame. In the 
oxidizing flame it gives a red bead. Copper and its 
compounds color the flame green. 

Confirmatory Reactions. Dissolve the bead in nitric 
acid. A blue solution results. Dilute and pass in 
hydrogen sulphide gas. This gives a black precipi- 



32 CUE MIS TR Y AND ME TALL URGY 

tate of copper sulphide, CuS, not readily soluble in 
ammonium sulphide (distinction from arsenic, anti- 
mony and tin). Filter and digest with nitric acid. 
Again filter, and to the filtrate add ammonium 
hydroxide to alkaline reaction. This gives a deep blue 
solution readily decolorized by potassium cyanide, a 
double cyanide of copper being formed. If hydrogen 
sulphide is now added to the solution no precipitate 
of sulphide is obtained (method of separating copper 
and cadmium). 

CADMIUM. Symbol, Cd. Combining weight, 112. 
Specific gravity, 8.66. Melting point, 320° C. Cad- 
mium is a white, crystalline metal, somewhat softer 
than aluminum and harder than tin. It resembles tin 
in its general appearance, and crackles like tin when 
crushed. It is quite malleable and ductile but not 
very tenacious. Cadmium does not readily tarnish ex- 
cept in an atmosphere of hydrogen sulphide gas, due 
to the formation of cadmium sulphide, CdS. When 
heated to a low red heat it burns, forming cad- 
mium oxide, CdO. It is somewhat uncommon in the 
metallic condition and forms few compounds of im- 
portance. Cadmium is soluble in hot dilute hydro- 
chloric or sulphuric acid, but more soluble in nitric 
acid, cadmium nitrate, Cd(N0 3 ) 2 , being formed. 

Alloys. Fusible alloys and amalgam-alloys. As 
a constituent of the latter cadmium has fallen into 
disfavor, owing in part to its tendency to disintegrate 
and tarnish in the mouth. Cadmium amalgamates 
readily. 



APPLIED TO DENTISTRY. 33 

Chief Ore. Greenockite, CdS, found more or 
less associated with zinc. Reduced by heating with 
carbon and refined by distillation. 

Blowpipe Tests. On charcoal cadmium burns 
without melting, giving an incrustation of reddish 
brown cadmium oxide, CdO. 

Confirmatory Reactions. Dissolve some of the 
metal in nitric acid, dilute with water and add 
hydrogen sulphide gas. A yellow precipitate of 
cadmium sulphide, CdS, is obtained, resembling 
in color the corresponding precipitate of arsenic but 
distinguished from the latter by its insolubility in 
ammonium sulphide. The addition of potassium 
cyanide, previous to hydrogen sulphide gas, does not 
interfere with the precipitation of cadmium as cad- 
mium sulphide (distinction from copper). 

ALUMINUM. Symbol, Al. Combining weight, 
27. Specific gravity, 2.58. Melting point, 700° C. 
Aluminum resembles tin in color and silver in hard- 
ness and tenacity. When pure it does not tarnish in 
the air nor in the presence of hydrogen sulphide gas. 
At a high temperature it oxidizes, forming aluminum 
oxide, A1 2 3 . Aluminum is one of the lightest met- 
als, and at the same time it rivals steel in strength. 
It is malleable and ductile, but becomes brittle upon 
working, and must be frequently annealed. The best 
temperature for working is between 100° and 150° C. 
The conducting power of aluminum for heat is about 
one-third and for electricity about two-thirds that of 
silver. In addition to the natural products referred 



34 CHEMISTRY AND METALLURGY 

to later, aluminum forms few compounds of impor- 
tance. Common alum has the composition K 2 S0 4 . 
A1 2 (S0 4 ) 3 + 24H 2 0. Aluminum is insoluble in cold 
nitric and slowly soluble in cold sulphuric acid. Hot, 
concentrated nitric acid dissolves it slowly. It dis- 
solves readily in hydrochloric acid, forming aluminum 
chloride, A1 2 C1 6 , and in alkali solutions, as potassium 
hydroxide, in this case forming an aluminate,K 2 A1 2 4 . 
In the presence of sodium chloride, organic acids 
attack aluminum somewhat. 

Alloys. Aluminum bronze, aluminum steel, Her- 
cules metal. Aluminum and silver form an important 
alloy used in making physical and chemical instru- 
ments. Pure aluminum as well as the alloy of 
aluminum and copper, i. e., aluminum bronze, is often 
used as the base for artificial dentures. Aluminum 
unites with mercury under certain conditions. The 
product is not stable, but decomposes into aluminum 
oxide and mercury, evolving heat. When moisture 
is present an aluminum amalgam greatly increases in 
volume and evolves hydrogen, due to the decomposi- 
tion of the water. This same phenomenon is observed 
when alloys containing as little as one to two per cent 
of aluminum aje amalgamated. Owing to the facts 
just stated aluminum is not a desirable constituent 
of amalgam-alloys, although it is sometimes added. 

Chief Ores. Bauxite, A1 2 3 +3H 2 0, cryolite, 
Na 3 AlF 6 , orthoclase, KAlSi 3 8 . The reduction is 
very complicated, and not yet entirely satisfactory. 
Probably the best strictly chemical method consists 



APPLIED TO DE APIS TRY. 35 

in heating the double chloride of aluminum and 
sodium with metallic sodium. 

AlCl 3 .NaCl + 3Na = Al + 4NaCl. 

Electrolytic methods have displaced this for com- 
mercial purposes. 

Blowpipe Tests. On charcoal aluminum melts 
quite readily, but does not flow into a bead. If 
heated on asbestos in the oxidizing flame and then 
moistened with cobalt nitrate, it appears blue upon 
cooling. 

Confirmatory Reactions. Dissolve the metal in hy- 
drochloric acid. To a portion of the solution add 
potassium hydroxide. A white, gelatinous precipitate 
of aluminum hydroxide, Al 2 (OH) 6 , is formed, soluble 
in an excess of the reagent, forming potassium alu- 
minate, K 2 A1.,0 4 . To another portion add ammonium 
hydroxide; the same precipitate is formed, but in this 
case it is not soluble in an excess of the reagent. 

Aluminum Silicates. Among the important min- 
erals containing aluminum silicate, and occurring with 
the exception of the last named in enormous quantities 
in nature are felspar, kaolin, clay and ultramarine. 
The first three substances enter into the composition 
of porcelain, brick, earthenware, etc., while the last is 
an important coloring matter. 

Felspars. The more common felspars are ortho- 
clase, KAlSi 3 8 , and albite, NaAlSi 3 8 . By the 
action of natural agencies these substances are decom- 
posed and large beds of more or less pure clay result. 

Kaolin or China Clay. This is the purest form of 



36 CHEMISTRY AND METALLURGY 

aluminum silicate found in nature. It has the approx- 
imate composition Al 4 (Si0 4 ) 3 +4H 2 0. 

Clays. Ordinary clays are impure varieties of alu- 
minum silicate. They are often highly colored with 
compounds of iron. Clay mixed with considerable 
calcium carbonate is commonly called marl. Other 
clays of indefinite composition are loam, yellow ocher, 
Fuller's earth, etc. 

Ultramarine. This is a substance highly valued 
as a coloring matter. It consists of a silicate of 
sodium and aluminum together with certain com- 
pounds of sulphur. As already stated, it is found in 
limited quantities in nature and was formerly very 
expensive, but is now produced artificially in great 
quantities. In addition to the blue, a green, a red and 
a yellow can be produced. 

Porcelain. In the manufacture of porcelain, kaolin 
is used. When mixed with water it can be made into 
a plastic mass, capable of being molded into any 
required form. Articles made from clay alone, how- 
ever, are liable to crack on drying, due to included 
water. This difficulty is overcome by adding some 
variety of silica (silex), which renders the mass more 
open and more easily desiccated. To compensate 
for the loss of tenacity occasioned by adding silica, a 
certain quantity of felspar is added. This vitrifies 
and acts as a cement. The ingredients are thoroughly 
mixed in the required proportions, molded, dried, and 
then subjected to a red heat. This gives a porous, un- 
glazed product. The article is next covered with the 
glazing material and burned again, at a white heat. 



APPLIED TO DENTISTRY. 37 

This produces the glaze. Glazing materials usually 
consist of the same materials as compose the body of 
the porcelain, mixed with a large proportion of fel- 
spar to render them very fusible. Porcelain is colored 
by means of various metallic oxides. In the making of 
dental porcelain a relatively high proportion of the 
felspar is used and the desired shades of enamel are 
obtained by the use of finely divided platinum, tita- 
nium oxide, purple of Cassius, etc. 

ZINC. Symbol, Zn. Combining weight, G5.3. Spe- 
cific gravity, 7.14. Melting point, 450° C. Zinc is a 
bluish white metal, not readily tarnished in airor water. 
When heated to a low red heat it burns with a 
bluish flame, forming zinc oxide, ZnO. Ordinarily 
zinc is lacking in malleability and ductility. Between 
100° and 150° C., however, it can be rolled into sheets 
and drawn into wire. At 200° C. it becomes so brittle 
that it can be powdered. In dentistry zinc is widely 
employed in making dies upon which metal plates 
are swaged. Its low melting point, its hardness and 
its toughness render it particularly adaptable to this 
purpose, although its tendency to contract upon 
cooling is objectionable. After being melted several 
times the metal often becomes very brittle owing to 
the presence of dissolved zinc oxide or to contamina- 
tion with iron from the ladle in which it is melted. 
In this condition zinc may be purified by throwing 
some dry ammonium chloride upon its surface when 
in the molten state. The tenacity of zinc is twice 
that of lead. Its most important compound is zinc 



38 CHEMISTRY AND METALLURGY 

oxide, widely used as a pigment and in dental cement 
powders, etc. Zinc dissolves in all common acids, 
forming the following well-known substances: Zinc 
chloride, ZnCl 2 , zinc sulphate, ZnS0 4 , and zinc 
nitrate, Zn(NO s ) 2 . The impure varieties of zinc and 
those alloyed with copper or platinum are acted upon 
by acids more readily than the pure metal. Like 
aluminum, zinc dissolves in alkali solutions; for 
example, in potassium hydroxide, forming a zincate, 
K 2 ZnO s . 

Alloys. Zinc is a constituent of brass, various 
solders, amalgam-alloys, etc. It amalgamates, the 
product being used in preserving the zinc plates in 
batteries. Zinc is also widely used in coating iron, 
forming the well-known and useful galvanized iron. 

Chief Ore. Zinc blende, ZnS. Reduced by roast- 
ing and then distilling with carbon. Zinc is usually 
associated with arsenic in nature, so that commercial 
zinc and zinc oxide will seldom be found free from 
this impurity. 

Blowpipe Tests. Zinc does not melt on charcoal 
but burns, giving an incrustation of zinc oxide, ZnO, 
yellow while hot, white when cold. If moistened 
with cobalt nitrate the mass becomes green. 

Confirmatory Reactions. Dissolve some zinc in 
hydrochloric acid and add potassium hydroxide. A 
white precipitate of zinc hydroxide, Zn(OH) 2 , forms 
and readily redissolves like aluminum hydroxide in 
an excess of the reagent, potassium zincate, K 2 Zn0 2 , 
being formed. If then ammonium sulphide is added, 
a white precipitate of zinc sulphide, ZnS, is obtained. 



APPLIED TO DENTISTRY. 89 

IRON. Symbol, Fe. Combining weight, 56. 
Specific gravity, 7.70-7.84. Melting point of gray 
cast iron, 1275° C, and of cast steel, 1375° C. The 
physical properties of iron vary with the method of 
manufacture. Chemically pure iron is soft, lustrous 
and silver gray in color. Air and moisture are very 
destructive to iron, producing hydrated ferric oxide, 
Fe 2 3 .3H 2 (variable), commonly known as r//;/. To 
preserve iron it is painted, tinned, galvanized, etc. 
When strongly heated in the air iron becomes 
coated with a layer of magnetic oxide, Fe 3 4 . In 
tenacity iron exceeds all other metals but nickel and 
cobalt. It is one of the most ductile metals, but 
somewhat deficient in malleability, ranking with 
zinc. When heated, however, its ductility and mal- 
leability are greatly increased. Iron is very infusible 
except at the highest heat of the blast furnace. It 
possesses the peculiar property of softening at white 
heat, and in this condition can be welded. Pure iron 
is attracted by the magnet, but does not retain magnet- 
ism. Permanent magnets are made of steel. The 
common oxides of iron are ferrous oxide, FeO, and 
ferric oxide, Fe 2 3 . Well-known compounds of iron 
are ferric chloride, Fe 2 Cl 6 , and ferrous sulphate, 
FeS0 4 , both used in medicine. Iron dissolves in all 
common acids, forming with hydrochloric, ferrous 
chloride, FeCl 2 , and with sulphuric, ferrous sulphate, 
FeS0 4 . With nitric acid iron forms ferric nitrate, 
Fe g (NO,),. 

Alloys. Iron forms few alloys of importance ex 
cept its combination with nickel, manganese, chro 



40 CHEMISTRY AND METALLURGY 

mium, etc., in steels. Tinned and galvanized iron 
have already been referred to. An iron amalgam can 
be obtained by adding sodium amalgam to a solution 
of an iron salt. 

Chief Ores. Hematite. Fe 2 3 , magnetite, Fe 3 4 , 
and clay ironstone, FeC0 3 . Iron is reduced by heat- 
ing in special blast furnaces. The ore, with alternat- 
ing layers of coal and limestone or other flux, is 
placed in the top of a tall cylindrical furnace. An 
intense heat is applied and air is blown in through 
pipes known as tuyeres. Clay, sand and other impu- 
rities unite with the limestone and form a fusible slag. 
The iron is reduced, and uniting with carbon and sili- 
con forms a fusible mass, which settles in the furnace 
and later is molded in sand troughs into pigs. Iron 
thus obtained is known as pig iron or cast iron, and 
contains carbon, sulphur, silicon, etc. 

Wrought iron is made by subjecting pig iron to the 
puddling process, which consists in melting the iron 
in contact with air, and thus oxidizing the carbon, sil- 
icon and other constituents. Wrought iron is very 
malleable, and increases in this respect as the per- 
centage of carbon decreases. 

Steel. The most important and rapid process for 
making steel is that known as the Bessemer process. 
It consists in burning out the carbon and silicon in 
cast iron by blowing air through the molten metal, and 
then adding pure cast iron in such a quantity as to in- 
troduce the required percentage of carbon. The steel 
is next cast into ingots. For many purposes the 
addition of small quantities of phosphorus, manga- 



APPLIED TO DLXTIS1KY. 41 

nese, chromium, tungsten, etc., improves its quality. 
Steel is grayish white in color and is capable of 
taking a high polish. When heated and cooled sud- 
denly it becomes extremely hard and brittle. By 
properly reheating hardened steel to certain tempera- 
tures below red heat and then cooling suddenly, it is 
possible to produce steel of any required hardness. 
This is known as tempering. 

Blowpipe Tests. On charcoal iron is infusible. Iron 
compounds reduced on charcoal with sodium carbon- 
ate give the magnetic oxide, Fe 3 4 , which is attracted 
by the magnet. 

Confirmatory Reactions. Dissolve some iron in 
hydrochloric acid. Add chlorine water and boil. * To 
a portion add ammonium hydroxide to alkaline reac- 
tion. A reddish precipitate of ferric hydroxide, 
OH) Q , is formed. Filter, dissolve in hydrochloric 
acid and add potassium sulphocyanate. A red solu- 
tion is formed. This is a very delicate test. To 
another portion add potassium hydroxide; ferric 
hydroxide is again formed, but unlike the correspond- 
ing precipitates of zinc and aluminum, it is insoluble 
in an excess of the reagent. 

MANGANESE. Symbol, Mn. Combining weight. 
Specific gravity, 7.14-7.20. Manganese as a 
metal is not very common, and is used chiefly to im- 
prove the quality of steel. It is hard, brittle and re- 
sembles cast iron. It oxidizes in the air and decom- 

*To make chlorine water add dilute hydrochloric acid to a 
fragment of potassium chlorate in a test tube and boil. 



42 CHEMIST R Y AND ME TALL URGY 

poses water. Manganese forms several oxides, most 
important of which is manganese dioxide, Mn0 2 , used 
in making oxygen and in the manufacture of steel. 
Another important compound is potassium perman- 
ganate, KMn0 4 . Common salts of manganese are 
the chloride, MnCl 2 , the nitrate, Mn(N0 3 ) 2 , and the 
sulphate, MnS0 4 . 

Alloys. Manganese forms several alloys of im- 
portance, among which is cupro-manganese, used in 
making manganese bronze, manganese brass, etc. 

Chief Ore. Pyrolusite, Mn0 2 . Reduced by heat- 
ing at a high degree with carbon. 

Blowpipe Test. Fuse a small quantity of man- 
ganese dioxide on a platinum foil with plenty of so- 
dium carbonate and potassium nitrate. A green mass 
results, composed chiefly of sodium and potassium 
manganate, Na 2 Mn0 4 and K 2 Mn0 4 . 

Confir?natory React io?i. Dissolve some manganese 
sulphate in hot water. Add ammonium hydrox- 
ide to alkaline reaction and then ammonium sulphide. 
A flesh colored precipitate of manganous sulphide, 
MnS, is formed. Filter and fuse this precipitate on 
platinum as indicated above and obtain a green mass. 

CHROMIUM. Symbol, Cr. Combining weight, 
52.1. Specific gravity, 5.9-7.3. Melting point, above 
platinum. Chromium is a nearly infusible crystalline 
powder, light green in color. It is quite uncommon 
in the free state, but forms many important com- 
pounds, such as potassium dichromate, K 2 Cr 2 7 , and 



APPLIED TO DENTISTRY. 43 

chrome alum, K 2 S0 4 .Cr 2 (S0 4 ) 3 + 24H 2 0, analogous 
in composition to common alum. Other important 
compounds, widely used as pigments, are lead chro- 
mate, PbCr0 4 , known as chrome yellow, and chromic 
oxide, Cr 2 3 , known as chrome green. 

Alloys. Chromium forms no alloys of importance. 
When added in the proportion of 0.5 to 0.75 percent 
to steel it makes a hard product known as chrome 
steel. 

Chief Ore. Chrome ironstone, FeO.Cr 2 3 . Metal- 
lic chromium is commonly reduced from chromic 
chloride by electrolysis. 

Blowpipe Tests. Compounds of chromium, as 
chrome alum, give, when fused on platinum with 
sodium carbonate and potassium nitrate, a yellow 
mass. Boil this mass with water in an evaporating 
dish. Filter. Acidify the filtrate with acetic acid 
and add lead acetate. A yellow precipitate of lead 
chromate, PbCr0 4 , is formed. 

Confirmatory Reaction. Dissolve some chrome 
alum in water, and to a portion add ammonium hy- 
droxide. A grayish precipitate of chromic hydrox- 
ide, Cr 2 (OH) 6 , appears. To another portion add 
potassium hydroxide; chromic hydroxide appears, 
but redissolves in excess, a compound analogous to a 
zincate being formed. Boil the solution and the pre- 
cipitate reappears, unlike the corresponding com- 
pounds of zinc and aluminum. Filter and fuse on 
platinum as indicated above. 



44 CBEMISTR Y AND ME TALL URGY 

NICKEL. Symbol, Ni. Combining weight, 58.7. 
Specific gravity, 8.9. Melting point, 1450° C. Nickel 
is a highly lustrous, yellowish white metal. It is 
somewhat harder than iron, very brittle, but ren- 
dered so malleable by the presence of a small quan- 
tity of magnesium that it can be rolled, drawn into 
wire, welded, etc. It is more tenacious than iron and, 
like iron, it is attracted by the magnet. Nickel does not 
oxidize in the air at ordinary temperature, but is 
slowly tarnished in dry hydrogen sulphide gas, nickel 
sulphide, NiS, being formed. Nickel dissolves slowly 
in hydrochloric or sulphuric acid, but readily in nitric, 
forming nickel nitrate, Ni(N0 3 ) 2 . 

Alloys. Varieties of bronze, German silver 
and substitutes for German silver. An important 
compound of nickel and steel has lately attracted 
much attention as an armor plate material. Nickel 
is widely used in plating. It does not amalgamate 
directly. A nickel amalgam can be made by adding 
sodium amalgam to the solution of a nickel salt. 

Chief Ore. Nickel blende, NiS. Reduced after 
roasting by heating with carbon. Nickel and cobalt 
occur associated in nature. 

Blowpipe Tests. Metallic nickel is infusible on 
charcoal. Nickel compounds, as nickel nitrate, give 
a clear bead which is violet while hot and yellowish 
brown when cold. 

Confirmatory Reactions. Dissolve some nickel in 
nitric acid. A green solution is formed. Add am- 
monium hydroxide and ammonium sulphide. A 



APPLIED TO DENTISTRY. 45 

black precipitate of nickel sulphide, NiS, is formed, 
nearly insoluble in hydrochloric acid. Dissolve the 
precipitate by boiling in nitric acid; filter. Evapo- 
rate the solution nearly to dryness, and wash down 
the sides of the dish with water. Add potassium cya- 
nide until a precipitate appears and redissolves, then 
an excess of sodium hypobromite and boil. A black 
precipitate of nickelic hydroxide, Ni 2 (OH) 6 , is formed. 

COBALT. Symbol, Co. Combining weight, 59. 
Specific gravity, 8.9. Melting point, 1500° C. Cobalt 
is a white metal with a cast of red. It is harder than 
iron and more tenacious, but resembles this metal in 
malleability and ductility. It tarnishes slowly in 
moist air, but readily in moist hydrogen sulphide, 
cobalt sulphide, CoS, being formed. Like iron and 
nickel it is attracted by the magnet. As a metal 
cobalt has little application in the arts. Smalt is an 
important compound of cobalt, used as a pigment. 
A so-called sympathetic ink can be made by dissolv- 
ing cobalt chloride, Co0 2 -f6H 2 0, or the nitrate, 
Co(N0 3 ) g +6H g O, in water. These solutions, when 
used in place of ink give an invisible line. When 
the paper is slightly warmed the writing becomes 
visible, due to the dehydration of the cobalt salt. 
The writing will again become invisible if allowed 
to absorb moisture. 

Alloys. Cobalt forms few alloys of importance. 
Like nickel and iron, it does not amalgamate directly. 

Chief Ores. Smaltite, CoAs 2 , and cobaltite, 



46 CHEMISTRY AND METALLURGY 

CoS 2 .CoAs 2 . Reduced by carbon in various ways. 
Its reduction is a difficult matter. 

Blowpipe Test. Cobalt is infusible on charcoal. 
Its compounds, when fused in a borax bead made in 
the loop of a platinum wire, impart to the bead 
a deep blue color. If the bead is too strongly 
saturated it will appear black. 

Confirmatory Reactions. Dissolve some cobalt 
nitrate in water. Add ammonium hydroxide and 
ammonium sulphide. A black precipitate of cobalt 
sulphide, CoS, nearly insoluble in hydrochloric acid, 
is formed. This precipitate gives the characteristic 
blue borax bead. 

BARIUM. Symbol, Ba. Combining weight, 137. 
Specific gravity, 3.75. Melting point, 475° C. Barium 
is a silver white metal, ductile and malleable. It oxi- 
dizes rapidly in air or in water and never has been 
obtained in the coherent state. Many compounds of 
barium are important. Barium sulphate, BaS0 4 , 
commonly known as heavy spar> used to adulterate 
paints; barium chloride, BaCl 2 ,used as a reagent in 
the laboratory to detect sulphuric acid and sulphates; 
barium dioxide, Ba0 2 , used in the preparation of hy- 
drogen dioxide solutions. Barium forms no alloys. 
It can be made to unite with mercury by galvanic 
action, but the product is very unstable. 

Occurrence. Heavy spar, BaS0 4 . Metallic barium 
is obtained by the decomposition of the chloride by 
an electric current. 

Blowpipe Test, Barium compounds, as barium 



APPLIED TO DENTISTRY. 47 

chloride, when held in the outer part of the Bunsen 
flame, on a platinum wire, impart to the flame a yel- 
lowish green color. 

Confirmatory Reactions. Dissolve some barium ni- 
trate in water. Add ammonium hydroxide and am- 
monium carbonate. A white precipitate of barium 
carbonate, BaC0 3 , is formed. Filter, dissolve in acetic 
acid. Divide into two portions. To one add sulphuric 
acid and obtain a white, insoluble precipitate of 
barium sulphate, BaS0 4 . To the second portion add 
potassium dichromate and obtain a yellow precipitate 
of barium chromate, BaCr0 4 . 

STRONTIUM. Symbol, Sr. Combining weight, 
87.6. Specific gravity, 2.4. Melting point, red heat. 
Strontium is a slightly yellow metal, quite ductile and 
malleable, and harder than gold. It oxidizes rapidly 
in air and decomposes water. Its common com- 
pounds are strontium chloride, SrCl 2 , strontium sul- 
phate, SrS0 4 ,and strontium nitrate, Sr(N0 3 ) 2 . The 
last named is used to make red fire. Strontium 
compounds are of little value in the arts. The 
metal does not enter into the composition of alloys. 
Like barium, it can be made to unite with mercury. 

Occurrence. Strontianite, SrC0 3 , and celestine, 
SrS0 4 . Metallic strontium is prepared in the same 
manner as barium. 

Blowpipe Test. Strontium compounds impart to 
the flame a beautiful crimson color. 

Confirmatory Reaction. Dissolve some strontium 



4 8 CHE MIS TR Y AND ME TALL UR G Y 

nitrate in water. Add ammonium hydroxide and 
ammonium carbonate. A white precipitate of stron- 
tium carbonate, SrCO s , is formed. Filter, and dis- 
solve this precipitate in acetic acid. To a portion of 
this solution add a weak solution of potassium sul- 
phate and obtain a white precipitate of strontium 
sulphate, SrS0 4 . To the second portion add potas- 
sium dichromate. No precipitate is formed (dis- 
tinction from barium). 

CALCIUM. Symbol, Ca. Combining weight, 40. 
Specific gravity, 1.57. Melting point, red heat. Cal- 
cium is a pale yellow metal, soft as zinc, malleable 
and very ductile. Calcium, like barium and strontium, 
has no practical application. In moist air it oxi- 
dizes, and in water it produces a violent evolution of 
hydrogen. Compounds of importance are calcium 
oxide, CaO, commonly called lime; calcium hydroxide, 
Ca(OH) 2 , commonly called slaked lime; calcium 
carbonate, CaCO s ; calcium sulphate, CaS0 4 , known 
as plaster of Paris; calcium hypochlorite, Ca(C10) 2 , 
bleaching powder; and calcium chloride, CaCl 2 . Cal- 
cium can be made to unite with mercury to form an 
unstable amalgam. 

Occurrence. Gypsum, CaS0 4 + 2H 2 0; limestone, 
CaCO s . Metallic calcium is prepared in the same 
manner as barium. 

Blowpipe Test. Compounds of calcium, as cal- 
cium chloride, impart to the flame a yellowish red 
color. 



APPLIED TO DENTISTRY. 49 

Confirmatory Reactions. Dissolve some calcium 
nitrate in water, add ammonium hydroxide and carbon- 
ate. A white precipitateof calcium carbonate, CaCO s , 
is formed. Filter, dissolve in acetic acid and to a 
portion add a weak solution of potassium sulphate; 
no precipitate appears (distinction from strontium). 
Next add ammonium hydroxide and ammonium oxa- 
late. A white precipitate of calcium oxalate, CaC 2 4 , 
is formed. To a second portion of the calcium solu- 
tion add potassium dichromate. No precipitate is 
formed (distinction from barium). 

MAGNESIUM. Symbol, Mg. Combining weight, 
24.3. Specific gravity, 1.75. Melting point, 500 ~ C. 
Magnesium is a white, hard, malleable and ductile 
metal. It can be rolled into ribbon and drawn into 
wire. It oxidizes slowly in air, but when heated above 
its melting point burns with a dazzling white light, 
the oxide, MgO, being formed. Common compounds 
of magnesium are magnesium oxide, MgO, commonly 
known as magnesia; magnesium carbonate, MgC0 3 ; 
magnesium sulphate, MgS0 4 , commonly called Ep- 
som salt. Magnesium is soluble in all common acids. 
It forms no alloys of importance, but can be made to 
form a somewhat unstable amalgam. The metal is 
employed to furnish the flash light in photography. 

Chief Ore. Magnesite, MgC0 3 . Found as Epsom 
salt in many spring waters. The metal is produced 
by fusing the chloride with sodium: 

MgCL+2Na=Mg+2NaCL 



50 CHEMISTR Y AND ME TA LLURGY 

Blowpipe Tests. Magnesium when heated on char- 
coal or in the Bunsen flame burns with a white light, 
the oxide, MgO, being formed. If this powder is 
dampened with cobalt nitrate and strongly ignited 
on charcoal it becomes pale rose in color. 

Confirmatory Reactions. Dissolve a piece of magne- 
sium in nitric acid, add ammonium hydroxide. A white 
precipitate appears, which redissolves in ammonium 
chloride. Add sodium phosphate. A white precipitate 
of ammonium magnesium phosphate, NH 4 MgP0 4 , is 
formed. 

POTASSIUM. Symbol, K. Combining weight, 
39.11. Specific gravity, 0.86. Melting point, 62.5° C. 
Potassium is a soft, plastic metal possessing a white 
metallic luster when freshly cut. It oxidizes in the 
air, and violently decomposes water, forming an alka- 
line solution, potassium hydroxide, KOH, and lib- 
erating hydrogen. For this reason it is kept under 
petroleum. Important compounds of potassium are 
the alkali just mentioned; potassium nitrate, KNO s , 
commonly called saltpeter; potassium chlorate, 
KC10 3 , both used in the manufacture of explosives; 
and potassium carbonate, K 2 CO s , pearl ash. Most 
potassium salts are soluble in water. Potassium 
unites with mercury to form an amalgam. 

Occurrence. Saltpeter, KN0 3 , more abundantly as 
potassium chloride, KC1. Reduced by fusing with 
carbon. 

K 2 C0 3 + 2C = 2K+3CO. 



Q w p > h 
a 5 3 



P" B M 
5 B 



^ O 

S. ^ B t 

o £ a " 



3- <t 



O <"& 



B 65 ft} 

o 3 

L- B 3 



APPLIED TO DENTISTRY. 



51 



Blowpipe Test. Potassium compounds, as potas- 
sium nitrate, when heated in the Bunsen flame on 
platinum wire and viewed through blue glass, give a 
violet flame. The object in using a blue glass is to 
shut out other flames, particularly sodium, which tend 
to obscure that of potassium. Potassium does not 
precipitate with any of the ordinary reagents. 

SODIUM. Symbol, Na. Combining weight, 2 3. 
Specific gravity, .972. Melting point, 95.6° C. Sodium 
resembles potassium in its properties. It must be 
kept under oil. Important compounds of sodium 
are sodium hydroxide, NaOH, caustic soda; sodium 
chloride, NaCl, common salt; sodium carbonate, 
Na 2 C0 3 , soda; sodium bicarbonate, NaHCO s ; so- 
dium nitrate, NaN0 3 , Chili saltpeter; sodium sul- 
phate, Na 2 S0 4 , Glauber's salt; and sodium borate, 
Na 3 B 4 O 7 +10H 2 O, borax. Anhydrous borax is 
known as borax glass. Most salts of sodium are 
soluble in water. Sodium forms an amalgam similar 
to that of potassium. 

Occurrence. Common salt, NaCl, Chili saltpeter, 
NaNO s , and in various other forms. Reduced by 
fusing with carbon. 

Na 2 C0 3 + 2C = 2Na+3CO. 

The preparation of sodium is a problem of great 
importance owing to its extensive use in reducing 
aluminum. 

Blowpipe Test. Sodium compounds color the 
flame a bright yellow, intercepted by blue glass. 
Like potassium, sodium is not precipitated by any of 
the common reagents. 



52 CHEMISTRY AND METALLURGY 

AMMONIUM. NH 4 . Molecular weight, 18. Am- 
monium is a hypothetical substance, not known in the 
free state but supposed to exist in the so-called am- 
monium salts and there perform the part of a metal. 
The support for the theory of the existence of this 
substance lies in the following facts: When sodium 
amalgam is thrown into a concentrated solution of 
ammonium chloride a spongy, metallic mass rises to 
the surface of the liquid. This is commonly called 
ammonium amalgam; and it is generally supposed 
that in this amalgam the ammonia gas and hydrogen 
exist united as NH 4 , for when an attempt is made to 
separate the mercury by heat the substance decom- 
poses into ammonia gas, N H 3 , hydrogen and mercury. 
Compounds of ammonium are ammonium hydroxide, 
NH 4 OH, commonly called ammonia water; ammonium 
chloride, NH 4 C1, often called sal ammoniac; am- 
monium nitrate, NH 4 NO s ; ammonium carbonate, 
(NH 4 ) 2 C0 3 ; ammonium sulphide, (NH 4 ) 3 S, and 
ammonium oxalate, (NH 4 ) 2 C 2 4 . Nearly all am- 
monium salts are soluble in water, and are volatil- 
ized by heat, in some cases with decomposition. In 
most of their chemical properties' these salts are anal- 
ogous to the salts of the alkalies proper, the group 
(NH 4 ) acting as a single metal, for example, as 
K or Na. 

Blowpipe Tests. The common salts, as ammonium 
chloride, when heated on charcoal or in a test tube 
vaporize, undecomposed, yielding dense white fumes. 
This is not true of ammonium nitrate, which when 
heated gives off water and nitrous oxide, N g O, com- 
monly called laughing gas. 



APPLIED TO DEXTISTRY. 53 

Confirmatory Reactions. Ammonia gas is recognized 
by its odor and by its power of turning red litmus 
paper blue. Note, however, that ammonium chloride 
possesses no odor. Dissolve some in water, add a 
strong solution of potassium hydroxide and boil. 
Ammonia gas, NH 3 , is liberated and can be detected 
by its odor or by its action on moist red litmus paper. 

GOLD. Symbol, Au. Combining weight, 197. 
Specific gravity, 19.26-19.31. Melting point, 1075° C. 
Gold is a yellow, lustrous metal not affected by air, 
by moisture or by sulphur and its compounds — prop- 
erties which have made it of great use for ornaments, 
from the remotest time. The color of gold is often 
modified, however; in the molten state it is green, 
when precipitated from a solution it is often brown, 
becoming yellow again when fused, and in the form 
of foil it transmits a green light. In malleability and 
ductility gold surpasses all other metals. It can be 
hammered into foil y^Ao °f an inc ^ in thickness and 
drawn into wire so fine that one mile of it will weigh 
less than a gram. Gold is nearly as soft as lead and 
about as tenacious as silver. Owing to its softness in 
the pure state, it must be alloyed to give it sufficient 
hardness to resist wear when used for coinage or 
jewelry. In alloying, copper and silver are used. Cop- 
per makes gold reddish in color, harder, more fusible 
and less ductile and malleable. Silver hardens gold, 
affects its malleability less than any other metal, but 
greatly modifies its color.' The addition of five per 
cent of silver makes an appreciable difference in the 



54 CHE MIS TR Y AND ME TALtURG V 

color, while fifty per cent destroys it. Varieties of 
gold alloyed with varying proportions of silver bear 
the names of yellow gold, green gold and pale gold. 
Alloys other than those mentioned are of little value. 
The presence of small quantities of lead, bismuth 
or antimony in gold makes it very brittle and greatly 
affects its color and luster. As little as 0. 05 per cent of 
lead or of antimony impairs its malleability and 
slightly greater quantities render it unworkable. 
From the facts just stated it is apparent that in work- 
ing gold great care must be exercised to prevent it 
from becoming contaminated with base metals, partic- 
ularly those mentioned. Thus after annealing, while 
the metal is still hot, it never should be placed upon 
a lead table top or brought in contact with any metals 
which are liable to alloy with it at comparatively 
low temperatures. After gold plates are swaged they 
should be carefully cleaned to remove adhering par- 
ticles of die metal which would diffuse into them 
upon annealing. This can be done by "pickling" 
in dilute nitric acid,* or by polishing with pumice 
stone on a brush-wheel. 

In the preparation of gold foil perfectly pure gold 
is usually used. It is first rolled into ribbon about 
ji- - of an inch in thickness, then cut into pieces an 
inch square and hammered between sheets of tough 
paper or vellum, and finally animal membrane, 

*An error often made by the student consists in " pickling " 
the plate in sulphuric acid to remove bits of die metal. It should 
be remembered that lead, antimony and certain other metals 
commonly employed in alloys for dies are insoluble in this acid. 



APPLIED TO DENTISTRY. 55 

termed gold-beater's skin, until it is about j^YtfTr °f 
an inch in thickness. These sheets of gold are next 
cut and made into books. Gold foil is used in 
dentistry for filling teeth. Two varieties, the cohesive 
and the noncohesive^ are commonly employed. The 
cohesive is simply pure gold which, when firmly 
packed in the cavity of the tooth by means of plug- 
gers, becomes welded owing to its characteristic 
cohesive property. The cohesiveness of this variety 
of gold is greatly diminished by the accumulation of 
moisture and gases upon its surface. By properly 
annealing, however, in the flame of a spirit lamp, in a 
muffle, or preferably upon a sheet of mica or metal, 
this property can be almost entirely restored. In the 
case of noncohesive gold union does not take place 
between the different pieces. This result is probably 
attained by slightly alloying or by subjecting the 
pure foil to the action of some gaseous substance 
which becomes deposited on its surface. The process 
of manufacturing noncohesive gold is a trade secret. 
Gold is insoluble in hydrochloric, sulphuric or 
nitric acid, but soluble in potassium cyanide, in free 
chlorine and in aqua regia, gold chloride, AuCl 3 , 
being formed in the last two cases. 

Alloys. Gold coin, gold plate, gold solders, etc. 
Gold unites very readily with mercury. The fine- 
ness of gold is usually expressed in carats. Pure gold 
is twenty four carats, or 1000 fine; twenty-two carat 
gold contains twenty-two parts of pure gold and two 
of other metal, and may be expressed as 916.6 fine. 
When a gold-silver or gold-copper alloy contains less 



56 CHEMISTRY AND METALLURGY 

than twenty-five per cent of gold, nitric acid will dis- 
integrate it; but when the gold is over this amount, 
sufficient silver or copper to bring the proportion of 
gold down to that stated must be fused with it 
before the acid will completely remove the alloying 
metal and leave the gold in a pure state. This is 
known as quartation. 

Chief Ores. Gold is usually found in the metallic 
state, often as nodules or nuggets. Its chief sources 
are quartz veins and alluvial deposits. In the first 
case the ore is crushed into a fine powder and the 
gold separated by amalgamation. Subsequently the 
amalgam is placed in iron retorts and the mercury is 
removed by distillation. Mining of this kind is com- 
monly called vein mining. In the second case the gold 
is washed with water in a "cradle," or pan. The 
gold being heavy remains mixed with sand and gravel, 
while the lighter substances are washed away. It 
then may be further separated from impurities by 
amalgamation, as indicated above. This is commonly 
known as placer ?nining. A modification of placer 
mining is hydraulic mining. It consists in directing a 
stream of water under high pressure against the 
mountain side, thus washing down and carrying away 
the loose gold-bearing earth and depositing the gold 
in sluices. 

After obtaining the gold by any of the foregoing 
processes it must be refined.* This may be done 
in several ways, for example by quartation or by dis- 

*See Chapter XII. 



APPLIED TO DENTISTRY. 57 

solving in aqua regia and precipitating the gold by 
some reducing agent, as ferrous sulphate. 

2AuCl 3 +6FeS0 4 =2Fe s (S0 4 ) 3 +Fe 2 Cl 6 +2Au. 

Other processes of extracting gold from its ores 
are chlorination and cyanide. In both processes the 
ore is crushed, oxidized in a reverberatory furnace 
and placed in large wooden vats. It is then treated 
with chlorine gas or leached with a solution of 
potassium cyanide. In the former case the gold is 
converted into the chloride, and after being dissolved 
in water is treated with ferrous sulphate to precipitate 
the gold as shown above. In the latter case the gold 
is dissolved by the cyanide solution and then pre- 
cipitated by means of an electric current. 

Blowpipe Tests. Gold remains a bright yellow 
after fusing on charcoal. In the melted state the 
bead appears green, and if allowed to cool undis- 
turbed, first turns dark on the surface, then suddenly 
"flashes, " becomes yellow and solidifies. This is 
more noticeable with large masses. 

Confirmatory Reactions. When a solution of stan- 
nous and stannic chlorides is added to gold chloride, 
AuCl 3 , a purple precipitate of unknown composition, 
commonly called purple of Cassius, is formed. Upon 
adding a solution of ferrous sulphate to gold chloride 
a dark brown precipitate of metallic gold results. 

PLATINUM. Symbol, Pt. Combining weight, 195. 
Specific gravity, 21.5. Melting point, 2000° C. 
Platinum is a tin white metal, not affected by 



58 CHEMISTRY AND METALLURGY 

air, moisture or hydrogen sulphide. It is infusible 
except in the oxyhydrogen flame, and not acted upon 
but by few substances; hence its wide use in the arts 
and sciences, particularly in chemistry, for crucibles, 
wire, etc. When made into crucibles, etc., it is usu- 
ally alloyed with iridium, thus increasing its hardness, 
melting point and resistance to reagents. Like iron, it 
can be welded at white heat, and by means of the oxy- 
hydrogen blowpipe it can be soldered autogenously, 
i. e., with itself. Platinum is more tenacious than 
silver, about as malleable as tin, and more ductile 
than other metals except gold and silver. Platinum 
wire can be drawn to T2 Vo °f an inch in diameter. 
In the melted state platinum, like silver, absorbs 
oxygen, which in being expelled causes " spitting." 
Finely divided platinum, particularly spongy platinum, 
possesses the peculiar property of condensing gases 
upon its surface. It can absorb many times its own 
volume of oxygen, hydrogen and other gases. Spongy 
platinum is made by igniting ammonium platinic 
chloride. Platinu??i black is a variety of finely divided 
platinum, often used in dentistry to color the enamel 
of artificial teeth. It may be prepared by dissolving 
platinum in aqua regia, evaporating the excess of 
acid, diluting with water and adding this solution to 
a boiling solution of glycerine and potassium hydrox- 
ide, or by boiling platinic chloride with a strong 
solution of potassium hydroxide and adding grape 
sugar. Platinum is insoluble in the common acids 
and dissolves more slowly than gold in aqua regia, 
forming platinic chloride, PtCl 4 . 



APPLIED TO DENTISTRY. 59 

Alloys. Platinum is used, alloyed with rare met- 
als, as indicated above. It enters somewhat into the 
composition of dental alloys. It unites with most 
metals, but forms no combination, when compact, 
with mercury. Platinum sponge, however, forms an 
amalgam when triturated in a warm mortar with 
mercury and acetic acid. A small proportion of 
platinum in gold renders this metal very elastic. 

Chief Ore. Platinum is found in the metallic 
form alloyed with certain rare metals, as palladium, 
rhodium, iridium, osmium, etc. The metal is not 
usually separated completely from these metals, but 
made into a pure alloy with them by fusing in a fur- 
nace heated by an oxyhydrogen blowpipe. 

When pure platinum is desired, the ore is first 
treated with nitric acid to dissolve any copper or iron 
present and then with dilute aqua regia. The plati- 
num dissolves and is precipitated from this solution 
as ammonium platinic chloride by ammonium chlo- 
ride. Upon being heated, this compound is decom- 
posed and the finely divided platinum resulting is 
converted into the compact variety by mixing with 
water and molding under high pressure and finally 
welding at a white heat. 

Blowpipe Test. Platinum is infusible on charcoal 
with the ordinary blowpipe flame. 

Confirmatory Reactions. Platinum dissolves slowly 
in aqua regia and is precipitated from this solution 
by alcohol and ammonium chloride as ammonium 
platinic chloride, (NH 4 ) 2 PtCl 6 , a yellow, crystalline 
precipitate. 



i 



60 CHEMISTR Y AND ME TALL URGY 



CHAPTER III, 



QUALITATIVE CHEMICAL ANALYSIS. 

Having become acquainted with some of the phys- 
ical and chemical tests which serve to distinguish 
one metal from another, the student next proceeds to 
apply these tests so that the metals, when existing in 
the form of complex mixtures, may be separated and 
identified. As already seen, it is not a difficult matter 
to distinguish between the metals when existing alone 
either in the metallic state or in solution; thus metal- 
lic silver or a silver solution is easily distinguished 
from the corresponding forms of lead. If, however, 
these metals exist in an alloy or in a complex solution 
the tests outlined in Chapter II. must be applied in a 
certain definite order. Unfortunately, each metal does 
not have a test solution or reagent of its own that can 
be added to a complex substance and identify that 
metal under all conditions. On the contrary, the 
addition of a reagent may be responded to by several 
metals, and it follows that the test for a metal is free 
from uncertainty only when it is definitely known that 
other metals responding to the same test are absent. 
It is evident, then, that qualitative analysis, far from 
being an application of tests without regard to order, 
is a systematic scheme whereby a metal is separated 



APPLIED TO DENTISTRY. 61 

in such a manner as to leave no doubt concerning 
its identity. Further, to illustrate, in the Confirmatory 
Reactions of the metals in Chapter II., it was observed 
that a silver solution gave, with hydrochloric acid, a 
white precipitate of silver chloride and this was called 
a test for silver. It was further observed, however, that 
lead and certain mercury solutions gave a similar 
white precipitate with the same reagent; and for this 
reason the test for silver is not final unless it is defi- 
nitely known that these metals are absent. Beyond 
the fact, however, that these precipitates are alike 
in color, and are produced by the same reagent, they 
do not resemble one another. Lead chloride dis- 
solves in hot water while the chlorides of silver and 
mercury do not. Silver chloride dissolves readily in 
ammonium hydroxide while mercurous chloride 
blackens. Thus is offered a method of positively 
identifying these metals, whether alone or in complex 
mixture. 

In the case just cited hydrochloric acid did not 
precipitate the metals in the metallic form but as 
chlorides, insoluble compounds of these metals. This 
is uniformly the case in qualitative analysis. There 
are few cases in which metals are precipitated as 
such. The reagent generally forms with the metal 
in solution a compound insoluble in the menstruum, 
hence it precipitates. As a rule in qualitative anal- 
ysis, the substance, if not already in solution, is dis- 
solved by some solvent, as water or acid, before the 
tests are applied. 



62 CHEMISTR Y AND ME TALL UKGY 

GROUPING OF THE METALS. 

As seen in the foregoing illustration, silver, lead 
and mercury are precipitated from their solutions as 
chlorides by means of hydrochloric acid. On this 
fact is based a method for separating these metals 
from all others, as they are the only ones forming 
insoluble precipitates with this acid. If, then, hydro- 
chloric acid is added to a mixture containing a great 
number of metals and a white precipitate appears, it is 
evident that some of these metals are present. On add- 
ing sufficient acid they will be completely precipitated 
and can be removed from the solution by filtration. 
If to the filtrate from which these metals have been 
removed hydrogen sulphide is added, another precip- 
itate may appear, which may contain the following 
metals, viz., arsenic, antimony, tin, bismuth, copper, 
cadmium and some lead and mercury. This, again, 
can be separated from the solution by filtration. 
Hence, by the successive application of reagents 
capable of removing from the original solution certain 
metals, all are separated into groups. In this manner 
the analysis of a complex solution is somewhat sim- 
plified, as it is known that each group contains only a 
limited number of metals. It next remains to submit 
each group to a special series of tests in order to de- 
termine the individual metals present. Reagents like 
hydrochloric acid and hydrogen sulphide are com- 
monly called group reagents. In the following table 
are given the five groups of metals and their corre- 
sponding group reagents. It should always be borne 
in mind that in actual analysis each group is removed 



APPLIED TO DENTIS'IRY 



63 



in its order; thus hydrochloric acid is first added to 
the solution, the resulting precipitate removed by 
filtration, then to the filtrate hydrogen sulphide is 
added, etc. If a group reagent fails to produce a 
precipitate, no metals of that group are present, and 
the solution is taken to the next group. 

GROUP TABLE. 



Group Reagents. 

From the original 
solution HC1 pre- 
cipitates 



Lead as PbCl 2 (white) 
Silver as AgCl (white) 
Mercury (ous) Hg 2 Cl 2 (white) 



Group I. 



From Group I. 
nitrate H 2 S^ 
precipitates 



From Group II 
nitrate 



NH 4 OH 



(NH 4 
cipitate 



and 
2 S pre- 



From Group III. fil 
trate (NH 4 ) 2 CO 
precipitates 



Arsenic as As 2 S 3 (yellow) 
Antimony as Sb 2 S 3 (orange red) 
Tin as SnS or SnS 2 (brown or yel 
Bismuth as Bi 2 S 3 (black) [low) 
Copper as CuS (black) 
Cadmium as CdS (yellow) 
Mercury (ic) as HgS (black) 
Lead as PbS (black) 

Iron as FeS (black) 
Aluminum as Al 2 (OH) 6 (white) 
Chromium asCr 2 (OH) 6 (green) 
Manganese as MnS (flesh color) 

j Zinc as ZnS (white) 

j Nickel as NiS (black) 

I Cobalt as CoS (black) 

Barium as BaCO, 3 (white) 



Group II. 



Group III 



Strontium as SrSQ 3 (white) > Group IV. 



Calcium as CaCO s (white) 



Group IV. filtrate will contain 



[Magnesium 
j Sodium 
1 Potassium 



1 



[Ammonium 



j>Group V. 



Note. — Separate portions of the Group IV. filtrate are used 
in testing for Mg, Na and K. NH 4 is looked for in the original 
solution. 



64 CHEMISTR Y AND ME TALL URG Y 



CHAPTER IV.* 



ANALYSIS OF GROUP I. 
Separation of Lead, Silver and Mercury. 

To the unknown solution add hydrochloric acid, 
stirring vigorously, in sufficient quantity to com- 
pletely precipitate Group I. This is best determined 
by adding the reagent as long as a precipitate seems 
to be formed, and then filtering. If a drop more of 
acid produces further precipitation, add more and 
filter again through another paper. Keep the fil- 
trate for Group II Wash the precipitate with 
cold, distilled water. Always reject washings unless 
directed to the contrary. Heat some water in a test 
tube and pour over the precipitate on the filter. Col- 
lect the water in a second test tube as it passes 
through. Reheat, pour over again and collect as 
before. 

Lead chloride is soluble in hot water and if 
present in the precipitate will be removed and 
can be tested for in the water solution by adding 
sulphuric acid. Lead salts give with sulphuric acid 
a fine white precipitate of lead sulphate, PbS0 4 . 
To the remainder of the precipitate on the filter, which 

*In order fully to understand the reactions employed in 
qualitative analysis consult the Confirmatory Reactions given 
under each metal in Chapter II. 



APPLIED TO DENTISTRY. 65 

may contain the chlorides of silver and mercury(ous), 
add ammonium hydroxide. Silver chloride is soluble 
in the latter and can be tested for in the ammo- 
niacal solution by acidifying with nitric acid. The 
presence of silver is indicated by the appearance of 
a white, curdy precipitate of silver chloride, AgCl. 
Finally, if mercurous chloride is present in the pre- 
cipitate it will remain on the filter paper as a black 
residue, mercurous ammonium chloride, NH 2 Hg 2 Cl, 
after the above treatment with ammonium hydroxide. 
This black residue is sufficient evidence of the 
presence of mercury. 

After following these directions until familiar with 
the details, it will be found more convenient to use 
Table I. on page 80, which is an abbreviated outline 
of the process just given.* 

*The form of report to be submitted by the student after com- 
pleting the analysis of an unknown substance is shown in the 
Appendix, Section II. 



66 CHEMISTR Y AND ME TALL URG Y 



CHAPTER V, 



ANALYSIS OF GROUP II. 

Separation of Arsenic, Antimony, Tin, Bismuth, 
Copper, Cadmium, Mercury and Lead. 

To the filtrate from Group I. add hydrogen sul- 
phide gas as long as a precipitate seems to form. 
Filter and pass more gas into the filtrate. Under 
certain conditions some of the metals of this group 
are slow in precipitating. If a precipitate again ap- 
pears, filter and keep the filtrate for Group III. Wash 
the precipitate once with water and proceed to deter- 
mine the metals. The color of the precipitate often 
gives some idea as to its composition. The sul- 
phides of lead,* mercury,*)" bismuth and copper are 
black, those of cadmium and arsenic, light yellow, 
that of antimony, brick red, and that of tin, dark 
brown. Remove precipitate and paper from the 
funnel, place in a porcelain evaporating dish and 
cover with yellow ammonium sulphide. Heat gently, 
i. e., "digest" for some time and filter. The sulphides 



*If lead was found in Group I. it will usually appear here 
owing to the slight solubility of lead chloride in cold water and in 
hydrochloric acid. 

fThe mercury referred to here is a mercuric compound. 
Mercuric salts, unlike mercurous, are not precipitated by hydro- 
chloric acid in Group I. 



APPLIED TO DENTISTRY. 67 

of arsenic, antimony and tin are soluble in am- 
monium sulphide, and will now be found in this fil- 
trate, while the balance of the sulphides remain as a 
residue on the filter paper. Proceed as follows with 
the ammonium sulphide solution : To it add hydro- 
chloric acid. If any of the three soluble sulphides 
are present they appear as a more or less highly 
colored precipitate. Filter and reject the filtrate. 
Redissolve this precipitate by digesting in a porcelain 
dish with chlorine water. 

As more or less sulphur is always present here, it 
will remain as a white or colored insoluble residue. 
Filter out any sulphur, boil to expel chlorine, and 
test for arsenic, antimony and tin as follows : In a 
hydrogen generator (see Fig. 25) place a few pieces 
of zinc and cover with hydrochloric acid. It is obvious 
that zinc free from arsenic must be used. When 
the hydrogen has run for a short time, pour the solu- 
tion to be tested for arsenic, antimony and tin into 
the generator through the funnel tube. Allow the gas 
from the generator to bubble into some silver nitrate 
solution in a test tube for five or ten minutes. Arsenic 
and antimony are converted by the nascent hydrogen 
into gaseous compounds, which pass into the silver 
nitrate, while the tin remains in the generator. A 
black precipitate in the silver nitrate indicates arsenic 
or antimony. Confirm by filtering and treating as 
follows : (Save the filtrate, as it may contain arsenic.) 
Wash the precipitate very thoroughly with water, di- 
gest in warm potassium hydroxide, filter, acidify with 
hydrochloric acid and add hydrogen sulphide. An 



68 CHEMISTR Y AND ME TALL URG V 

orange red precipitate, antimony sulphide, Sb 2 S 3 , in- 
dicates antimony. To the above filtrate, which may 
contain arsenic, add hydrochloric acid to remove the 
silver. Filter, reject the precipitate, which is silver 
chloride, and test the filtrate for arsenic by hydrogen 
sulphide. A yellow precipitate, arsenious sulphide, 
As 2 S 3 , indicates arsenic. Next turn to the generator 
and test its contents for tin. If the zinc is not entirely 
dissolved, add a little concentrated hydrochloric acid, 
and, when dissolved, filter a portion of the liquid in 
the generator and test it for tin by adding mercuric 
chloride. A white precipitate, mercurous chloride, 
Hg 2 Cl 2 , indicates tin. Return now to the residue 
which remained after treating the Group II. precipi- 
tate with yellow ammonium sulphide. This residue 
may contain the sulphides of mercury, lead, bismuth, 
copper and cadmium. Place it, together with the 
filter paper, in a porcelain dish and digest with 
nitric acid. Everything goes into solution except 
mercuric sulphide, which remains as a black residue. 
Filter, and treat the filtrate as indicated below. 
Test the black residue for mercury by dissolv- 
ing in aqua regia, boiling and adding stannous 
chloride. A white precipitate, mercurous chloride, 
Hg 2 Cl 2 , is final evidence of mercury. To the filtrate, 
which may contain the nitrates of lead, bismuth, 
copper and cadmium, add a few drops of sulphuric 
acid and evaporate nearly to dryness. Dilute with 
water in a beaker. A white precipitate, lead sulphate, 
PbS0 4 , indicates lead. Filter, and to the filtrate add 
ammonium hydroxide in excess of alkalinity. If 



APPLIED TO DENTISTRY. 69 

copper is present the solution will assume a deep 
blue color, sufficient evidence of copper, and in this 
solution will be distinguished a white, gelatinous pre- 
cipitate, bismuth hydroxide, Bi(OH) 3 , if bismuth is 
present. Further confirm by filtering and testing as 
follows : (Keep the filtrate to test for cadmium.) To 
the precipitate on the filter paper, supposed to be 
bismuth hydroxide, add stannitc* and if bismuth, it 
will immediately turn black. To the blue filtrate 
which remains to be tested for cadmium add potassium 
cyanide until the color disappears and then pass in 
hydrogen sulphide gas. If cadmium is present a 
yellow precipitate of cadmium sulphide, CdS, appears. 
It should be noted, however, that if copper is not 
present, indicated by a colorless solution, it is un- 
necessary to add potassium cyanide, but the filtrate 
from the precipitate of bismuth hydroxide can be 
tested at once for cadmium by passing into it hydro- 
gen sulphide gas. The purpose of adding potassium 
cyanide to the blue solution is to convert the cop- 
per into a form which does not precipitate with 
hydrogen sulphide, else the black copper sulphide 
formed would obscure the yellow of the cadmium 
sulphide. (Hereafter substitute Table II.) 

See note, page o<>. 



70 CHEMISTR Y AND ME TALL URGY 



CHAPTER VI 



ANALYSIS OF GROUP III.* 

• Separation of Zinc, Aluminum, Iron, Manganese, 
Chromium, Nickel and Cobalt. 

To the filtrate from Group II add a few 
drops of ammonium chloride, then ammonium 
hydroxide to alkaline reaction. The purpose of 
adding ammonium chloride is to keep magnesium, a 
fifth group metal, from precipitating here as an hydrox- 
ide. After the addition of ammonium hydroxide, a 
gelatinous precipitate of the hydroxides of iron, 
aluminum and chromium may appear. Disregard 
this and add enough ammonium sulphide to make the 
precipitation complete. Filter, and add to the filtrate 
a few more drops of ammonium sulphide to insure 
complete precipitation. Keep the filtrate for Group 
IV. Treat the precipitate as follows : Wash once 

*In case phosphates are present in the solution, a modifica- 
tion of this method must be employed, owing to the fact that 
barium, strontium, calcium and magnesium precipitate as phos- 
phates upon the addition of ammonium hydroxide. Phosphoric 
acid is detected by boiling a small portion of Group II filtrate 
first, to remove hydrogen sulphide, then with a drop of nitric acid 
and an excess of ammonium molybdate. A yellow precipitate is 
ammonium phospho-molybdate. Should phosphoric acid be 
found by the test just suggested, tre'at the filtrate from Group 
II. according to Table VI. instead of Table III. 



APPLIED TO DEXTISTRY. 71 

with water and then pour cold hydrochloric acid over 
it, returning the same portion of acid to the filter two 
or three times. A black residue, insoluble in hydro- 
chloric acid, indicates nickel or cobalt. Test this 
residue as indicated later. Evaporate the hydro- 
chloric acid solution, which may contain zinc, alumi- 
num, chromium, iron and manganese, nearly to dry- 
ness in a porcelain dish. Wash down the sides of 
the dish with water and add an excess of potassium 
hydroxide. Boil for a minute and filter. Iron, man- 
ganese, chromium and some nickel and cobalt are pre- 
cipitated as hydroxides, while zinc and aluminum are 
precipitated but redissolved by the alkali and will be 
found in the filtrate. Test the filtrate for zinc and 
aluminum. Divide into two portions. To one add 
ammonium sulphide. A white precipitate, zinc sul- 
phide, ZnS, indicates zinc. To the second portion 
add twice its volume of ammonium chloride, boil and 
let stand a few minutes. A white, flaky precipitate, 
aluminum hydroxide, AL OH ) fJ is evidenceof alumi- 
num. The precipitate obtained above with potassium 
hydroxide, test for iron, manganese and chromium 
as follows : Remove a small portion from the filter 
paper with a glass rod. Place it in a test tube and dis- 
solve in chlorine water. Boil to expel free chlorine 
and test for iron by adding potassium sulphocyanate, 
KCNS. A red coloration, Fe t CXS) 6 , is evidence of 
iron. Remove the remainder of the precipitate and 
the paper from the funnel, roll it up into a small 
mass, place it on a platinum foil and fuse with twice 
its bulk of potassium nitrate and sodium carbonate. 



72 CHE MIS TR V AND ME TALL URG V 

Make this fusion perfect, using the blowpipe if neces- 
sary. After cooling, the mass will be dark green in 
color if manganese is present, due to the formation 
of a manganate, K 2 Mn0 4 . Dissolve the mass in 
boiling water. Filter, acidify with acetic acid, boil 
and add lead acetate. A yellow precipitate of lead 
chromate, PbCr0 4 , will appear if chromium is present. 
A white precipitate will sometimes appear here due 
to the insufficient addition of acetic acid. This is no 
evidence of chromium. Return now to the black resi- 
due, which was insoluble in hydrochloric acid. Test 
it for cobalt first by means of the borax bead. A 
blue bead proves cobalt. To test for nickel dissolve 
the residue in dilute nitric acid by digesting in a 
porcelain dish. Filter and evaporate the filtrate 
nearly to dryness. Take up with a little water, add 
potassium cyanide until a precipitate forms and redis- 
solves, then an excess of sodium hypobromite. If 
nickel is present it shows itself as a dense black pre- 
cipitate of nickelic hydroxide, Ni 2 (OH) 6 . (Hereafter 
substitute Table III.) 



APPLIED TO DENTISTRY. 73 



CHAPTER VII 



ANALYSIS OF GROUP IV. 

Separation of Barium, Strontium and Calcium. 

To the filtrate from Group III. add ammonium 
carbonate. Warm and filter. Add a little more of 
the reagent to insure complete precipitation. If no 
further precipitate is formed keep the filtrate for Group 
V. Wash the precipitate of carbonates with water 
and dissolve in acetic acid, using very little and pour- 
ing it on several times. Everything dissolves. Add 
to this acetic acid solution an excess of potassium 
dichromate. A yellow precipitate of barium chromate, 
BaCr0 4 , appears if barium is present in the solution. 
Warm and filter. The filtrate can now be tested for 
strontium and calcium. Potassium dichromate being 
a colored reagent, the filtrate is always yellow if it is in 
excess, and the latter condition is essential to insure 
complete precipitation. It is well to first separate 
any calcium or strontium from the dichromate solu- 
tion. This is done by adding ammonium hydroxide 
until alkaline, and then reprecipitating strontium and 
calcium with ammonium carbonate. Filter, wash 
thoroughly to remove the colored liquid from the pre- 
cipitate and reject both washings and filtrate. Re- 
dissolve the precipitate with acetic acid as before, 
add a weak solution of potassium sulphate and allow 



74 CHEMISTRY AND METALLURGY 

the liquid to stand for ten minutes; a white precipitate 
is strontium sulphate, SrS0 4 . Filter. To the filtrate 
add ammonium hydroxide and ammonium oxalate. 
If calcium is present a fine, white precipitate of cal- 
cium oxalate, CaC 2 4 , will form. (Hereafter sub- 
stitute Table IV.) 



APPLIED TO DENTISTRY. 75 



CHAPTER VIII, 



ANALYSIS OF GROUP V. 

Testing for Hagnesium, Sodium, Potassium and 

Ammonium. 

With the exception of ammonium, the metals of 
this group should be looked for in the filtrate from 
Group IV. To test for magnesium take a small 
portion of Group IV. filtrate, add ammonium chlo- 
ride and hydroxide, and then sodium phosphate. A 
white precipitate, ammonium magnesium phosphate, 
NH 4 MgP0 4 , appears after a time if magnesium 
is present. Into another portion of the filtrate from 
Group IV. dip a clean platinum wire and hold in the 
flame. If sodium is present the flame above the wire 
will be colored a bright yellow. Again dip the wire into 
the solution, hold it in the flame and observe the flame 
through a piece of blue glass. A violet flame indicates 
potassium. The student should become familiar 
with the potassium flame by testing some solution 
known to contain potassium, as potassium sulphate. 
The object of using the blue glass, as already ex- 
plained, is to shut out any sodium color, which is 
usually so bright as to obscure small quantities of 
potassium. 

It is evident that ammonium cannot be looked 
for here, as its compounds have been employed as 



16 CHEMISTRY AND METALLURGY 

reagent several times during the course of the analysis. 
Therefore, take a portion of the original solution in a 
test tube, add potassium hydroxide to strong alkaline 
reaction; a precipitate may occur, but disregard it, 
and boil the contents of the test tube vigorously. 
Ammonium compounds are decomposed by the alkali 
and ammonia gas is liberated. This may be detected 
by its odor or by its action on damp red litmus 
paper. ( Hereafter substitute Table V.) 



APPLIED TO DENTISTRY. 77 



CHAPTER IX. 



TREATMENT OF HETALS AND ALLOYS. 

In previous chapters the analysis of complex mix- 
tures of metals in solution was considered. It often 
occurs in practical analysis, however, that instead of 
a mixture of metallic salts in solution the substance 
to be analyzed is a metal or a mixture of metals, 
such as an alloy. 

The analysis of such a substance usually consists 
in converting it into solution by some acid and then 
applying the ordinary qualitative scheme beginning at 
Group I. It is obvious that in this work such 
metals as barium, strontium, calcium and the alkali 
metals need not be looked for, as they do not enter 
into the composition of alloys. 

In every case a careful examination of the physi- 
cal propeities, such as color, crystalline form, fusibil- 
ity, etc., should precede an attempt to convert the 
substance into solution. Often the blowpipe reactions 
serve to identify the substance, at least in part. 
Thus, if a small piece easily fuses into a globule on 
charcoal, any of the fusible metals referred to in 
Chapter II. may be present. On the other hand, if the 
substance is infusible, iron, cobalt, nickel or platinum 
may be present. Further, the incrustation obtained 
may throw some light upon the presence of certain 



78 CHEMISTRY AND METALLURGY 

oxidizable metals. The next step is to convert the 
substance into solution. It was observed in Chapter II, 
that all the metals are not soluble in any single acid 
but that nitric acid is the most common solvent; hence 
nitric acid is generally used in this connection, as it 
dissolves all the metals except tin, antimony, gold 
and platinum. 

METHOD. 

Take a small quantity of the metal, prefer- 
ably in the form of filings or clippings, and treat 
with strong nitric acid in an evaporating dish. Ap- 
ply heat gently, adding small portions of acid occa- 
sionally to overcome the loss by evaporation until the 
substance is wholly dissolved or disintegrated. 

I. If the substance has completely dissolved, 
evaporate the solution almost to dryness to remove 
the excess of acid. Add considerable water and pro- 
ceed as in the analysis of solutions, starting with 
Group I. Should the solution become turbid upon 
diluting with water bismuth is likely present. Add 
enough nitric acid to remove this turbidity. 

II. If the substance has not completely dissolved 
in nitric acid, pour off the clear liquid, add more acid, 
boil and again pour off. Treat the clear solution as 
indicated in I. Wash the residue from the evaporating 
dish into a filter and then wash thoroughly with 
water. This insoluble residue may contain gold, 
platinum, tin or antimony, the last two in the form 
of metastannic and antimonic acids. Boil with con- 
centrated hydrochloric acid in an evaporating dish 
for ten minutes, then add water and boil. Filter, 



APPLIED TO DENTISTRY. 79 

and treat the filtrate for tin and antimony as indicated 
in Chapter V. If a dark residue remains after boiling 
with hydrochloric acid, gold or platinum may be 
looked for. 

Residue. Digest in aqua regia until dissolved. 
Gold and platinic chlorides are formed. Dilute with 
a little water and filter if not perfectly clear. Divide 
into two portions. 

1. Test one for gold. Dilute considerably and add 
a clear solution of ferrous sulphate. A brown precipi- 
tate of metallic gold will be formed if gold is present. 

2. Test the second portion for platinum by evapo- 
rating nearly to dryness and adding ammonium 
chloride and alcohol. After standing some time a 
yellow precipitate of ammonium platinic chloride will 
separate if platinum is present. 



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Chemical Technology Applied to 
Dentistry. 



88 CHEMISTRY AND METALLURGY 



CHAPTER X. 



ALLOYS. GENERAL CONSIDERATION. 

A chemical property of the metals, already referred 
to in Chapter I., is that of uniting with one another 
to form a class of compounds called alloys. As a rule, 
this term refers to a combination of two or more met- 
als effected by fusion. A class of alloys, however, 
commonly called amalgams, in which mercury is one 
of the constituents, may be produced not only by 
adding mercury to a molten metal, but also by the 
action of a metal on a salt of mercury, by the action 
of mercury on a salt of a metal, and, finally, by bring- 
ing a metal in contact with mercury. Although the 
term amalgam is applied to particular metallic com- 
pounds, it must not be inferred that they are distinct 
from alloys. Indeed, they differ in no way except 
that they contain mercury, which endows them with 
certain peculiar properties. Hence, in the following 
consideration, the general facts stated concerning the 
chemistry of alloys and the classification quoted from 
Matthiessen, apply to amalgams as well. 

The knowledge of alloys, although perfected to a 
high degree along certain lines, especially those which 
relate to their superficial properties and to their 
adaptability to the technical arts, must nevertheless 
be considered very incomplete from the standpoint of 



APPLIED TO DENTISTRY, 89 

chemistry. Indeed, it is still a matter of controversy 
whether alloys are true chemical compounds. It is 
probable that metals in many instances combine with 
each other in definite proportions. It is a difficult 
matter in most cases, however, to determine the 
chemistry underlying these combinations, since the 
compounds, if formed, dissolve in an excess of the 
melted metals, and seldom can be separated in crys- 
talline form. In a few instances alloys apparently 
possess definite chemical composition. Their forma- 
tion is attended by phenomena which characterize 
chemical change, such as heat and incandescence. 
Metallic crystals are at times formed, and in nearly 
all cases there is observed a variation in specific grav- 
ity and in melting point from the corresponding 
values of a mere mixture of the metals. Further- 
more, there are some instances of alloys found in 
nature showing the constituents in definite propor- 
tions. Thus an amalgam of silver occurs in which the 
metals are combined in the ratio of their combining 
weights, and hence can be represented by the for- 
mula HgAg. 

Although other evidence could be cited which 
would seem to support the theory of chemical union, it 
nevertheless must be admitted that whenever combi- 
nation takes place between metals the alteration of 
physical properties, which is a distinctive character- 
istic of chemical union, is not very pronounced. In 
the most unquestionably metallic compounds the 
properties which characterize metals, such as color, 
luster, hardness, conductivity, etc., although often 



90 CFIEMISTR Y AND ME TALL URG V 

modified, are still retained; and in alloying no such 
loss of identity takes place as occurs when a metal 
unites with a nonmetallic element, such as oxygen, 
chlorine, etc. Moreover, the affinity which binds the 
metals in an alloy is very feeble, and the state of com- 
bination is, therefore, easily affected by outside 
forces. Many alloys, including the most stable 
amalgams, are readily decomposed by heat, and some 
simply by air or by water. Not a few alloys separate 
into layers, especially if allowed to cool slowly, with 
the result that an ingot not at all homogeneous is 
formed. This phenomenon, which is a matter of 
great importance in refining certain metals and in 
preparing alloys for industrial purposes, is commonly 
called liquation. A good example is the separation of 
lead and zinc, two metals which apparently have little 
affinity for each other. If equal parts of these metals 
are fused and then thoroughly mixed and allowed to 
cool slowly in a deep mold they will be found to sepa- 
rate almost completely, only one and six-tenths per 
cent of zinc being retained by the lead. An important 
application of liquation in the refining of metals is 
shown in the separation of silver from lead by the 
Pattison method described on page 20. The author has 
had occasion to make some experiments with alloys of 
silver and tin, such as are commonly employed with 
mercury in filling teeth, and he finds that by keeping 
a perfectly homogeneous alloy of these metals in a 
molten state for one-half hour in a deep graphite 
mold a decided liquation results. This is shown by 
the fact that a large proportion of the silver employed 



APPLIED TO DENTISTRY. 1)1 

is found at the bottom of the ingot. In cases where 
liquation has occurred a more homogeneous alloy can 
be obtained by remelting. 

According to Matthiessen, it is probable that an alloy 
of two metals in a melted state is, first, a solution of 
one metal in another; or second, a chemical combi- 
nation; or third, a mechanical mixture; or fourth, 
a solution or a mixture of two or of all of the above. 

Physical Properties of Alloys. 

From the preceding study of the metals it may be 
observed that comparatively few possess properties 
which render them suitable to be employed in the 
pure condition in the arts and manufactures. By 
properly alloying a metal, however, with one or more 
others it is possible to obtain a new metal, as it were, 
which more nearly possesses the required properties 
than do the metals entering into its composition. 
Thus, attention has been called to the fact that gold 
and silver are too soft to be minted or to be used in 
jewelry, but that the addition of certain quantities of 
copper renders them harder and more capable of 
resisting wear. Copper, which in the pure state is 
too tough to be worked in the lathe, is converted when 
alloyed with zinc into the useful product known as 
brass, the properties of which make it particularly 
suitable for turning. Moreover, many metals, as 
arsenic, antimony, bismuth, manganese, chromium, 
etc., which alone are practically without value, confer 
certain desirable properties upon alloys. The changes 
in the properties of metals induced by alloying have 



92 CHEMIS TR Y AND ME TALL URGY 

been quite fully discussed in Chapters I. and II., but 
for the convenience of the student they are briefly 
reviewed here. 

COLOR, LUSTER AND SONOROUSNESS. 

Those metals which possess decided color, 
namely, copper and gold, are greatly modified by 
alloying, and often a colored alloy is obtained by 
combining two metals which possess no decided color. 
When ten per cent of aluminum is added to copper 
air alloy resembling gold in color is produced, and 
when antimony and copper in equal proportions are 
fused together a violet alloy is formed. 

The luster of a metal is often modified, and at 
times even destroyed by alloying. The case of gold 
alloyed with base metals is an example. 

A property possessed to only a slight degree by 
most metals, namely, sonorousness, is greatly in- 
creased in many instances by alloying. Thus copper 
and tin combined in certain proportions produce the 
alloy known as bell metal. Copper and aluminum 
also produce a very sonorous alloy. 

SPECIFIC GRAVITY. 

Contrary to what might be expected, alloys sel- 
dom possess a specific gravity which corresponds to 
the mean of the specific gravities of the constituents. 
In cases where a perfectly homogeneous alloy has not 
been obtained, as in liquation, the specific gravity 
will vary, of course, in different portions of the ingot. 



APPLIED TO DENTISTRY. 93 

FUSIBILITY AND CRYSTALLINE FORM. 

In most cases the melting point of an alloy is less 
than the mean melting point of its constituents. 
Indeed, it is not uncommon to find the melting point 
greatly below that of any of the metals employed in 
the alloy. Common soft solder, for example, melts 
more easily than either the tin or lead composing it. 
The compounds known as fusible alloys owe their great 
fusibility to the presence of bismuth, cadmium or 
mercury. Thus an alloy known as Rose's metal, 
composed of one part of lead, one part of tin and two 
parts of bismuth, melts at 95° C, or considerably 
below the temperature of boiling water. Another 
alloy, composed of eight parts of lead, fifteen parts of 
bismuth, four parts of tin and three parts of cadmium, 
melts at G5° C, the theoretical point shown by calcu- 
lation being 284° C. An alloy of the alkali metals, 
sodium and potassium, is liquid at ordinary temper- 
ature. 

Alloys often exhibit a crystalline form. Like 
metals, they become crystalline under the influence of 
percussion and other forms of mechanical working. 

MALLEABILITY AND DUCTILITY. 

These properties are almost always diminished 
and in many cases destroyed.. Even the union of two 
very malleable metals, as gold and lead, forms an 
alloy which is very brittle. Again, the combination 
of a brittle and a ductile metal produces an alloy 
which is low in ductility. Examples are the alloys 
of gold with antimony and bismuth, already referred 
to in Chapter II. 



94 CHEMISTRY AND METALLURGY 

HARDNESS, ELASTICITY AND TENACITY. 

The effect of alloying upon hardness has been 
already referred to. The alloy of gold and silver used 
for coin is a good example. 

The elasticity of certain metals may be increased 
by the addition of small quantities of other metals. 
An example is the alloying of gold with platinum. 

As a rule, tenacity is greatly increased by alloying. 
Thus the tenacity of copper is increased threefold by 
adding twelve per cent of tin.* The tenacity of iron 
compared with that of steel is in the ratio of one to 
two and one-half.* 

CHANGE OF VOLUME WITH TEMPERATURE. 

The coefficient of expansion of alloys with heat is 
approximately the average of the constituent values. 
However, a few decided variations from this rule have 
been observed. Thus a copper-tin alloy expands less 
than pure copper, although the expansion oi tin is 
considerably more than that of copper. 

SPECIFIC HEAT AND CONDUCTING POWER. 

The specific heat of an alloy is the mean of the 
specific heats of the metals composing it. 

In their power of conducting heat and electricity 
alloys do not in any case exceed the conductivity of 
the components. In fact, alloying generally results 
in reducing these properties. 

Chemical Properties of Alloys. 

The chemical properties of alloys do not differ 
materially from those of the metals constituting them. 

^Results obtained by Matthiessen. 



APPLIED TO DEXT1STRY. 95 

In certain instances the tendency to oxidize is 
increased by alloying. Alloys of lead and tin are 
oxidized more readily than either of the constituents. 
Alloys of silver and tin, those used with mercury for 
filling teeth, are exceedingly oxidizable, as will be 
shown later. Probably the most important and inter- 
esting change in the chemical properties ot certain 
metals after alloying is that shown by their action 
toward solvents. Silver, which by itself is readily 
soluble in nitric acid, becomes insoluble when alloyed 
with much gold. Indeed, as already stated, it is 
difficult to remove the silver completely from gold 
unless the latter constitutes less than twenty-five per 
cent of the alloy. Again, platinum, which by itself is 
insoluble in nitric acid, dissolves completely in this 
acid when alloyed with ten or twelve times its weight 
of silver. 

Preparation of Alloys. 

The method commonly employed in preparing 
alloys consists in fusing the proper proportions of 
the metals in a crucible. Usually graphite crucibles 
are used instead of those made of clay or sand, as 
they are less liable to crack when heated to a high 
temperature. The preparation of alloys is not, in 
most cases, a difficult matter, especially if certain 
important properties of the metals, such as fusibility, 
specific gravity, tendency to oxidize, etc., are kept in 
mind. Often the constituent metals are mixed and 
fused, particularly if they do not differ widely in their 
melting' points. In most cases, however, it is better 



96 CHE MIS TR Y AND ME TALL URGY 

to melt the metal possessing the .highest melting 
point and then add the others in the order of their 
fusibility. In order to prevent oxidation the surface 
of the metals should be covered with some substance, 
as borax or powdered charcoal; the heat should 
not be continued for any great length of time after 
the alloy is in a molten state; and finally, the tem- 
perature of the furnace should always be adapted to 
the fusibility of the metals, i. e., a heat sufficient to 
melt gold or silver should not be employed in mak- 
ing an alloy of tin and lead. In all cases care should 
be taken to prevent liquation, by stirring the alloy 
thoroughly with a pine stick and pouring into a cold 
mold. More details concerning the preparation of 
certain alloys will be given later. Although the 
directions given above are applicable in the prepara- 
tion of alloys in general, it should be borne in mind 
that no fixed rule can be followed in all cases. 






APPLIED PO DENTISTRY. 9? 



CHAPTER XI 



APPARATUS. 

Various forms of apparatus, some of which are not 
commonly included in the ordinary laboratory outfit, 
are essential to the work outlined in subsequent chap- 
ters. In order that the student may become some- 
what familiar with them at the outset, considerable 
space will be devoted to their description. 

I. Balances and Weights. 

Analytical Balance. (Fig. 2.) This is an ex- 
tremely delicate balance used in accurate chemical 
and physical work. The various parts are an upright 
pillar, on the top of which is a highly polished steel 
or agate plane. Resting on this plane and attached 
to the center of the beam is a V-shaped steel or agate 
knife edge about which the beam vibrates. At each 
end of the beam is attached another similar knife 
edge, in this case inverted (A), supporting a little 
stirrup with a steel or agate plane, and from this stir- 
rup is suspended the light wire frame carrying the 
scale pan. This form of rest and support is designed 
to minimize the friction and to increase the sensitive- 
ness of the instrument. In order to prevent the knife 
edges from being injured by constant wear or jar on 



98 



CHEMISTR Y AND ME TALL URGY 



the planes, the beam is raised and supported when 
not in use by a lever mechanism shown below the 
beam in the illustration. This is operated by a milled 




Fig. 2. 



handle in front. In addition to the beam support 
almost all balances have arms (see illustration) called 
"bumpers " which arrest the scale pans from beneath 
while the beam is resting upon its bearings. These 



APPLIED TO DEXTISTRY. 99 

are manipulated by an ivory push-button to the left 
of the milled handle. 

At the base of the pillar is an ivory scale in front 
of which swings the point of the index needle 
attached to the center of the beam. At each end of 
the beam is a small adjusting screw by means of which 
the beam is equipoised. The right side of the beam 
is usually divided into ten large and one hundred small 
scale divisions. By sliding a small piece of platinum 
wire, called a "rider," along the graduated portion 
the final adjustment of equilibrium is made while 
weighing and the use of inconveniently small weights 
is avoided. With a ten milligram rider each large 
division represents one milligram (0.001 gram), 
while a small division represents 0.0001 gram. When 
the rider rests on the tenth large division a ten milli- 
gram weight placed in the left-hand scale pan should 

exactly counterpoised. The rider is manipulated 
by the sliding rod shown above the beam and extend- 
ing outside the case. 

Weights. The metric system of weights (see Ap- 
pendix, Section I.) is used. The weights them- 
selves are enclosed in a wooden case (Fig. 3) and 
usually range from 100 grams to 10 milligrams. 
Weighings below ten milligrams are obtained by 
means of the rider. The gram weights are commonly 
made of brass and the fractions of a gram, of plati- 
num. After using a weight always return it to its 
proper place in the case but never employ the fingers 
in doing so. /// handling weights use a pair of tweezers. 



100 CHEMISTRY AND METALLURGY 

Special Directions. It should be borne in mind 
that the balance is a very delicate instrument and to 
give good results it must be used with the utmost 




Fig. 3. 

care. In weighing take a position directly in front 
of the index needle, raise the sliding window carefully 
and place the substance to be weighed in the left- 
hand scale pan. Estimate the weights required and 
place them in the right-hand pan while the beam is 
still supported. Carefully lower the support and 
leave the pans free to swing in order to see which 
carries the greater weight. Add or remove weights 
as necessary, always supporting the beam while doing 
so. When the smallest weights fail to counterpoise 
the substance employ the rider. Lower the window 
to avoid drafts of air, which might interfere with the 
accuracy of the weighing and cause the index needle 
to vibrate; perfect equilibrium is reached when it 
goes to an equal distance on each side of the central 
mark on the ivory scale. Support the beam, remove 
the weights and record the result. Many of the 
details involved in weighing cannot be described, 
and can be learned only by experience. 

When the balance is not in use keep the case 



APPLIED TO DEXTISTRY 



101 



closed, and never leave the beam unsupported. Re- 
move dust from the pans and other parts with a fine 
brush. Never bring corrosive substances in con- 




Fig. 4. 
tact with the pans; use a counterpoised watch crystal. 
Keep a beaker or other vessel containing dry calcium 
chloride inside the case to absorb moisture. Protect 
the balance from direct sunlight, from acid fumes and 
from the vibrations of the building. When not in a 
level position, which will be indicated by the spirit- 
level at the base of the upright pillar, adjust by means 
of the leveling screws underneath the case. The 
equipoise of the beam can be adjusted by the screws 



102 CHEMISTRY AND METALLURGY 

at each end. Study the balance and become familiar 
with its different parts and its manipulation. A good 
analytical balance will carry 100 grams in each pan 
and is sensible to one-tenth of a milligram. 

Pulp Balance. (Fig, 4.) This is a style of bal- 
ance adapted to weighing fluxes, metals for alloys, 
and to other uses in which considerable accuracy is 
required. 

It will be observed that the balance illustrated 
does not differ greatly in its general construction 
from the analytical balance; it is provided with knife 
edge bearings, movable pans, set screws and level, 
and an eccentric for raising the beam. Such a bal- 
ance is capable of carrying 300 grams in each scale 
pan, and of turning with a five milligram weight. 
Keep the pans free from dust and do not bring cor- 
rosive substances in contact with them. 



Fig. 5. 

Laboratory Scales. (Fig. 5.) These are scales for 

coarse weighing. Those illustrated (Harvard Trip) 

have porcelain plates in place of metal scale pans. 

Their capacity is 1000 grams (one kilogram). Weigh- 



APPLIED TO DEXTISTRY. 



103 



ingsfrom five grams to one-tenth of a gram can be made 
by using simply the beam and sliding weight in front. 

II. Furnaces* and Accessories. 

Raskins' Assay Furnaces. Very satisfactory fur- 
naces for assaying purposes and for use in refining 
and alloying on a comparatively large scale are those 
known as Hoskins' Hydro-carbon Assay Furnaces. 
The outfit, shown complete in the Frontispiece 
I Fig. 1 ), consists of a crucible furnace, a muflle 
furnace and a patent blowpipe, employing gasoline 
as fuel. The different parts are illustrated and de- 
scribed below. 




Fig. C. 

Crucible Furnace. (Fig. G.) This is a furnace in which 
crucibles are employed. Various sizes of Hoskins' 
crucible furnace are made. Size No. 1 is cylindrical 

* For descriptions of various furnaces not considered here 
refer to Essig's "American Text-book of Prosthetic Dentistry," or 
to the catalogues of Richards & Co., Chicago, E. H. Sargent & 
Co., Chicago, and of other dealers in chemists' and assayers' sup- 
plies. 



1 04 CHE MIS TR V AND ME TALL URGY 

in form, and contains a chamber six inches high and 
four inches in diameter. A convenient size (No. 4) 
and form for a large laboratory is that illustrated, 
containing a chamber six and one-fourth inches high, 
eight inches long and six and one-half inches wide, 
and heated by a No. 3 blowpipe, holding one gallon 
of gasoline. The furnace body is made of an infusible 
material, enclosed in a casing of sheet iron. At the 
left is shown the fire-hole or opening for the blast, 
and on top the chimney for the escape of the products 




Fig. 7. 
of combustion. The heat can be made to range from 
that of the Bunsen burner to that required to melt 
cast iron, and the maximum effect can be produced 
in ten minutes from the start. The advantages of 
Hoskins' furnaces over those employing solid or 
gaseous fuel are many; dust, ashes, smoke and radi- 
ated heat, connected with the use of coke and coal, 
are avoided, and a high degree of heat can be pro- 
duced in a very short time; unlike furnaces burning 
ordinary illuminating gas, the blast is automatic, not 
requiring the use of a blower. Finally, they can be 
used in places where gas is not obtainable. 



APPLIED TO DEXTISTRY. 



105 



Muffle Furnace. (Fig. 7.) This is a furnace used in 
the processes in assaying known as cupellation and 
scorification, and in other operations not requiring 
the heat of a direct flame, as enameling, etc. It 
consists of a furnace body in which is an arched 
clay enclosure known as a muffle. The Hoskins' fur- 
nace illustrated is heated from the rear by the blow- 
pipe used in connection with the crucible furnace. 
A convenient muffle furnace is one taking a muffle 
ten inches long, six inches wide and four inches high. 




Hydro-carl w Blowpipe. (Fig- 8.) The important 
parts of this apparatus are : A tank, T, which con- 
tains gasoline and compressed air, the latter being 
forced in by the pump, P; an automatic valve at A, 
which closes after each stroke of the pump and a cut- 
off valve, C, which closes completely the connection 
b t ween the pump and tank; a plug, F, removed when 
the tank is to be filled; a vent, V, for releasing the air 
pressure in the tank when the apparatus is not in use; 
a pipe, H, connecting the tank and the burner, D; a 
regulating valve, E, terminating in a fine point con- 



106 CHEMISTRY AND METALLURGY 

trolling the flow of gasoline; and two boxes, SS, 
packed to prevent leaking about the valves. 

To operate the blowpipe, unscrew F and fill the 
tank about two-thirds full of gasoline (74° Beaum£). 
Caution: Do not attempt to do this near the highly 
heated furnace or near any flame. Replace F, open C, 
give the pump six or eight strokes and close C. 
Bring the nose of the burner within two inches of the 



Fig. 9. 
fire hole in the furnace, and place a Bunsen flame 
under D. After ten minutes or so the gasoline in 
the burner tubes will become vaporized, and if E is 
slowly opened the gas will escape and can be ignited. 
Regulate the intensity of the flame by the pump and 
valve E. When the interior of the furnace has 
reached a bright red heat, quickly shut off E and 
immediately turn on again. When the furnace is 
hot enough the escaping gas ignites and burns inside 
the furnace. If ; however, the furnace is not hot enough 
the gas will fail to ignite. In such a case continue 
the first flame until the proper temperature is reached. 
There is no danger connected with the use of this blowpipe 
except through gross carelessness. 



APrLIED TO DENTISTRY. 



107 



Other Furnaces. Although an outfit like that just 
described is indispensable in many operations, a 
smaller furnace can be used to advantage in certain 
cases, particularly in alloying small quantities of 
metals, in calcining cement powders, etc., etc. In- 
deed, the furnaces illustrated and described below will 
meet most requirements of the student and the prac- 
ticing dentist. A very efficient and convenient fur- 
nace (Fig. 9) for melting 300 grams or less of metal 
is that made for dentists and jewelers by the Buffalo 
Dental Manufacturing Company. The furnace body 
is composed of a substance much lighter in weight 
than fire clay and said to possess only one-tenth its 
conducting power for heat. As illustrated, the 
apparatus consists of a furnace body with a cover and 
a blowpipe employing gas, all mounted on a cast iron 
base. With a gas supply pipe of three-eighths of an 




Fig. 10. 
inch and a good foot-blower (Fig. 24) sufficient heat 
can be obtained in ten or twelve minutes to melt 
cast iron. 

A furnace (Fig. 10) fully as efficient as the one 
just described and much more convenient in that it 



108 CHEMISTR Y AND ME TALL URG Y 

does away with the foot-blower, is that arranged by 
the author for the use of students in his laboratories. 
As will be observed, the furnace body is that illustrated 
in Fig. 9, mounted on a suitable tripod. The blow- 
pipe is a common gasoline paint burner with the tank 
removed some distance from the burner (the burner 
ordinarily is attached directly to the tank) in order 
to avoid heat from the furnace. To operate the 
blowpipe, unscrew the plug on top, fill the tank 
about two-thirds full of gasoline and replace the plug. 
Open the valve in the burner until the cup below is 
full of gasoline, then close; ignite the gasoline in the 
cup and when it is nearly burned, open the valve again. 
A strong, steady blast flame results. With a single 
filling, one quart of gasoline, this blowpipe will burn 
for two hours and during that time will require pump- 
ing up but once or twice. Some kerosene burners 
are now made which give about as hot a flame as 
those burning gasoline. These may be used unmodi- 
fied, as it is not necessary to separate the tank from 
the burner. 

Crucibles and Crucible Tongs. Crucibles (Fig. 11) 

in which metals are fused are made of 

graphite (black lead or plumbago), French 

clay, Hessian sand, etc. The so-called 

clay or sand crucibles are made in round 

and triangular forms and are suited to 

nearly all metallurgical operations. They 

Fig. 11. seldom can be used more than two or 

three times, as they crack when heated. Graphite 

crucibles last indefinitely and can be used in all 




IPPLIEP PO DENPISPRY. 



109 



fusions in which no oxidizing agents, as potassium 
nitrate, are used. A crucible for the small furnaces 
should be about two inches high and two inches 




Fig. 12. 

in diameter. The Iloskins' furnace takes four cru- 
cibles five and one-fourth inches high and three 
inches in diameter. Tongs for handling crucibles 
are illustrated in Fig. L2. 

rifiers and Scorifier Tongs. Scorifiers (Fig. 13) 
are shallow clay dishes used for scorifica- 
tions. The size ordinarily used is two and 
18. three-fourths inches in diameter. A con- 
venient form of scorifier tongs is that shown in Fig. 





Fig. 14. 

II. The forked arm fits the bottom of the scorifier 
and the straight arm extends across the top. 

Cupels and Cupel Tongs. Cupels (Fig. 15) are small 
articles made of bone ash and used in the 
process of cupellation. Bone ash absorbs 
the oxides of almost all metals, particularly 
those of lead; hence it is used in purifying 
gold and silver, which do not oxidize. A 
good cupel will absorb nearly its own weight of lead 
oxide. A convenient size for assaying purposes is one 




Fig. 15. 



110 



CHEMISTRY AND METALLURGY 



and a half inches in diameter. Cupel tongs are 
illustrated in Fig. 16. 



IT 



Zj 



Fig. 16. 



Button Mold, (Fig- l^-) The button mold, often 
called a slag or scorification mold, is generally used 




Fig. 17. 

in pouring scorification or other fusions in which a 
button-shaped ingot is desired. This mold should 
be kept clean and should be warmed on the furnace 
before using. 

Bullion Mold. (Fig. 18.) This is a convenient 

mold for casting a bar-shaped 
ingot of gold or silver bullion, 
solder, amalgam-alloy, etc. 
Fig. 18. It is provided with a sliding 

partition, so that any length below eight inches can 
be obtained. For many purposes a mold made of 
soapstone can be substituted for the one just described. 
When alloys are to be poured the mold should not 
be warmed, as an alloy should solidify quickly after 
pouring in order to prevent the metals from separat- 
ing. 




APPLIED TO DENTISTRY. 



Ill 



Upright Ingot Mold. (Fig. 10.) This gives an 
ingot about one eighth of an inch in 
thickness, which can be placed in 
the rolling mill without hammering 
out. The right-hand portion of this 
mold, as illustrated, is adjustable so 
that ingots of different widths can be 

Fig. 19. obtained. 




III. Miscellaneous Apparatus, 



CSEZSu© 




Fig. 20. 

Hand Rolling Mill. (Fig. 20.) When an ingot 
is to be rolled or laminated it is first annealed and 



112 



CHEMISTRY AND METALLURGY 



then passed between polished steel rollers, so con- 
trolled by pressure screws that they can be brought 
closer together each time the ingot is passed through. 
The thickness of the resulting plate is determined by a 




Fig. 21. 

gauge (Fig. 21). During the rolling the ingot should 
be annealed several times to prevent it from splitting 
at the edges. When a mill without geared pressure 

screws is employed care 
should be taken so to regu- 
late the rollers that a plate 
of the same thickness on 
both sides is produced, else 
F IG . 22. it will curve. However, 

should this happen, screw the rollers closer together 
on the thickest side, and continue rolling as before. 
Dp not reverse the plate, for this will crumple it. 




APPLIED TO DENTISTRY. 



113 



Iron Retort. (Fig. 22.) This is .used in distilling 
mercury from amalgams. A good substitute for this 
apparatus can be made at any plumber's shop. 




Blowpipe and Blower. In many operations, particu- 
larly in melting small quantities of gold, silver, etc., a 
blowpipe giving a higher temperature than the ordi- 
nary mouth blowpipe is required. For this purpose a 
brazing blowpipe (Fig. 23) can be used and the blast 
required can be obtained by a foot-blower (Fig. 24). 




Fig. 24. 

In operating attach the tube marked "gas M to the gas 
supply pipe by means of rubber tubing, and in the 
same manner connect the tube marked " blast " to the 
blower. By manipulating the valves as shown, both 



114 



CHE MIS TR V AND ME TALL URGY 



air and gas can be regulated and the* character of the 
flame can be controlled. 

Hydrogen Generator. ( Fig. 25.) This is also 
known as Marsh's apparatus. When used in testing 




for arsenic, antimony and tin, as indicated in Chapter 
V., a straight piece of glass tubing is attached to the 
exit tube by means of rubber tubing, as illustrated. In 
case Marsh's test for arsenic or antimony is to be 
made, a tube, drawn out until the opening in one end 
is about the size of the lead in a pencil (see figure), 
is substituted for the straight tube. 

Porcelain Crucibles and Pip est em Triangles. Fig. 
26 represents a porcelain crucible or 
capsule, with cover, used for many pur- 
poses in quantitative chemistry. They 
are designed to withstand high heat. A 
convenient size is one and one-half 
inches in diameter. Fig. 27 represents a triangle made 
of wire covered with pipestem. This is used to 
support the porcelain crucible while being heated. 




Fig. 26. 



APPLIED TO DENTISTRY. 



115 




Other utensils so common as to require no descrip- 
tion are : Anvil and vise, separate 
or attached; hammers, a light one, 
for hammering out gold and silver 
beads, and a heavy one for general 
use; pinchers with pointed nose 
for handling gold and silver beads; 
Fig. 27. shears for cutting metal; files, four- 

teen-inch bastard, for filing alloys; steel brush for 
cleaning files; magnet for removing iron filings from 
amalgam-alloys; sieves, forty, sixty, eighty meshes, 
for sifting filings; bolting cloth for sifting cement 
powders; mortars, a small w r edgwood mortar for mix- 
ing amalgams, a large mortar for grinding purposes; 
amalgam-filling instruments, spatula and glass plate 
for mixing cement, etc. 

IV. Apparatus for Testing Amalgams. 

Micrometer. The apparatus illustrated in Fig. 
28 has been designed by the author for the use 




Fig. 28. 

of students, in determining the expansion and contrac- 
tion of amalgams employed in filling teeth. It con- 




116 CHEMISTRY AND METALLURGY 

sists of a heavy base with two upright posts; between 
the latter is a horizontal axis with cup and pivot 
bearings, and attached to the center 
of this axis is a long steel needle 
which vibrates in front of a scale. 
Near the axis and attached to the 
Fig. 29. needle is a vertical plunger held in 

position by a guide extending out from one of the 
posts. It is evident that any vertical movement of this 
plunger will be greatly magnified at the point of the 
needle. The amalgam to be tested is packed in 
cavities in a steel block (Fig. 29), and the latter is 
placed in a guide attached to the base; the plunger 
is allowed to rest upon the surface of the amalgam 
and the point on the scale indicated by the needle is 
recorded. At various intervals during several days 
the block is returned to the apparatus and any expan- 
sion or contraction of the amalgam filling is noted by 
the movement of the needle along the scale. It is 
obvious that, owing to irregularities on the surface of 
the filling, the plunger should rest on the same point 
in every measurement taken. To accomplish this, a 
mark, corresponding to one on the guide, is made on 
the steel block when the first measurement is taken. 
At the left is seen a weight; this nearly counter- 
poises the needle and thus prevents the plunger from 
sinking into the amalgam while still soft. The scale 
is graduated in such a manner that one small division 
indicates -g 1 ^ of a millimeter (approximately T ^g^ inch) 
at the plunger; and as it is an easy matter to read 
to one-quarter of a scale division, an expansion or 



APPLIED TO DENTISTRY. 117 

contraction of ^\-§ millimeter (approximately -^Vo 
inch) can be accurately measured. 

Dynamometer. Fig. 30 represents an apparatus 
which may be used in determining the strength of 
amalgams and the change of form which they under- 
go when subjected to pressure, i. e., their so-called 
"flow." The apparatus consists of a steel spring, 
CC, in the form of a double bow. When this is 
compressed by the screw shown at the right a pressure 




Fig. 30. 

is communicated by a steel rod to the amalgam, 
which in the form of a block is placed between the 
end of the rod and the point of the stationary screw, 
J. By a cog mechanism attached to the vertical 
needle, S, the pressure exerted is recorded in pounds 
avoirdupois on the inner scale of the large dial, A. 
(The outer scale cannot be used in these tests, 



118 CHEMISTRY AND METALLURGY 

as it is designed for another purpose.) The vertical 
needle, S, in passing about the scale carries with 
it the second needle, also marked S. When the block 
of amalgam crushes the first needle is carried back 
by a coil spring to the zero mark, while the second, 
not being connected with the pinion, remains to indi- 
cate the stress applied. 

The amalgam to be tested is packed in the small 
cavities (lettered A, B, C, D) of the matrix (Fig. 
31). When these blocks of amalgam, which have the 





Fig. 31. 
dimensions 0.085 x 0.085 x 0.085 inch, have "set" they 
are removed by withdrawing one of the pins at the end 
and removing the sliding sections. After five days, tests 
may be made upon these samples. A block which 
is to be tested for strength is placed in the instru- 
ment and the screw turned until the sample crushes. 
The pressure necessary to do this will be recorded as 
already described, and this result may be taken 
as representing the crushing- strength of the amalgam. 
A block which is to be tested for flow is placed in the 
instrument in the same manner as above and a 
pressure equal to one quarter of that required to 



APPLIED TO DENTISTRY 



119 



crush the first sample is applied for some time. The 
flow of the amalgam is indicated in thousandths of 
an inch by the needle in the small dial, K. In all 
cases the time and pressure employed in bringing 
about a certain flow should be stated, since both 
these quantities are factors in the result. Finally, the 
flow is best stated in percentage. For example, if a 
block which originally was 0.085 inch in thickness is 
reduced to 0.0*765 inch by applying a pressure of fifty 
pounds for one hour, then the complete statement of 
the result would be : Pressure, fifty pounds; time, 
one hour; flow, ten per cent. 

V. Measuring Apparatus. 
Cylinders. (Fig. 82.) 




ni 



•? 



These are employed in meas- 
uring liquids when great 

accuracy is not required. 

They are made to contain 

1000 c. c. (cubic centimeters), 

500 c. c, 250 c. c, etc. E 

cubic centimeter is divided 

into tenths. 

Flasks. (Fig. 33.) These 

are used in place of cylinders 

in measuring liquids when 

great accuracy is required. 

They are made to contain 

1000 c. c, 500 c. c, 250 c. a, etc., of liquid 
at a certain temperature, usually 15° C. 

Pipettes. (Fig. 34.) These are used in meas- 
uring accurately a certain volume of liquid. The 





Fig. 33. 



Fig. 32. 



120 



CHEMISTRY AND METALLURGY 



liquid is drawn up by suc- 
tion to an indicating mark 
on the tube above the bulb 
and retained by closing the 
opening of the tube with 
the finger. The pipette 
illustrated delivers 50 c. c. 
Others are made to deliver 
100 c. c, 25 c. c, 10 c. c, 5 
c. c. and 1 c. c. Sometimes 
they are made after the form 
of a burette. 

Burettes, (Fig. 35.) These 
are made to deliver accurately 
volumes of liquid from 100 
c. c. down to one-tenth or 
one-twentieth of a cubic cen- 
timeter. Some are provided 
with a ground glass stopcock, 
others with a rubber tube, 
compressed by means of a 
clamp. The illustration shows 
a burette filled with a liquid, 
and mounted on an iron stand, 

I ready for use. Burettes and 
other glassware, when very 
dirty, can be cleaned with a 
mixture of potassium dichro- 
mate solution and sulphuric 
acid, after which they should be 
rinsed thoroughly with distilled 
water. 



Fig 
34. 



Fig. 35. 



APPLIED TO DEXTISTRY. 



121 




z \ 

- \ 
'- I 



« 



Q 



VI. Urine Analysis Apparatus. 
Urinometer. (Fig. 3G.) This is an instrument em- 
ployed in determining the specific gravity of urine. 

It floats in the urine, being 
held in an upright position by 
a bulb of mercury at the lower 
extremity. The degree on the 
graduated stem which corre- 
sponds with the surface of the 
urine is taken as the specific 
gravity. As a urinometer is 
graduated to give 
the correct reading 
only at a definite 
temperature, care 
should be taken to 
bring the urine to 
the required tem- 
perature before im- 
J± mersing the uri- 

nometer in it. This 
temperature, usu- 
ally 15.5° C. (60° 
F.) or 25 c C. (77° 
F.), is generally marked on the 
graduated stem of the instru- 
ment. 

Dor emus' Urcomeier. (Fig. 
37.) This is an apparatus used 
in determining the quantity of urea in urine. The 
apparatus is filled with a hypobromite solution and 




Fig. 37. 



Fig. 36. 



122 CHEMISTRY AND METALLURGY 

1 c. c. of urine is introduced into .the upright por- 
tion by means of the little pipette. The urea is 
decomposed by the hypobromite and the result- 
ing nitrogen accumulates in the graduated por- 
tion of the apparatus where the fraction of a gram 
of urea in 1 c. c. of urine is read off. The urine should 
always be introduced slowly in order to prevent 
a loss of nitrogen through the opening of the bulb. 



APPLIED TO DEXTISTRY. 123 



CHAPTER XII 



REFINING GOLD, SILVER AND MERCURY.* 

The refining of metals presents a problem of vast 
industrial importance, and one which has consider- 
able practical bearing upon dentistry. In order to 
illustrate the chemistry underlying this art, and at the 
same time to provide pure metals for subsequent use 
in making alloys, simple methods are here given for 
the student to follow in refining different forms of 
scrap gold and silver and in removing various impuri- 
ties from mercury. At least two grams of gold and 
twenty-five grams each of silver and mercury should 
be refined. t 

Refining Gold. 

Gold accumulated by the dentist and jeweler may 
be classified as follows: 

Class I. Clean scrap, as plate scrap, clippings, 
filings, etc. Waste of this character seldom needs 
refining — simply remelt, raising or lowering the carat 
if not of suitable fineness originally (see Appendix, 

^Material for this work, such as discarded gold jewelry and 
other scrap gold, silver watch cases, spoons, mutilated coin, 
waste dental amalgam, crude mercury, etc., can be obtained of 
refiners. 

f The form of report to be submitted upon the completion of 
this work is shown in the Appendix, Section II. 



124 CHEMISTR Y AND METALLURGY 

Section I.) and roll into plate. Follow the instruc- 
tions given in Method I. Should it be desired, 
however, to reduce the scrap to pure gold follow 
Method III. 

Class II Mixed scrap, as clippings, filings, solder, 
base metals, etc., containing little or no platinum. 
This scrap should be freed as far as possible of for- 
eign substances, then melted down as indicated in 
Method I., to remove base metals, and finally refined 
by Method III., in order to remove silver. In case 
the scrap contains much platinum, remove the latter 
mechanically, as far as possible, and then follow the 
instructions given in Method II. 

Class III Sweepings, as bench sweepings, resi- 
dues left after incinerating sandpaper strips or disks 
used in polishing gold, etc., etc. Waste of this char- 
acter will usually contain considerable foreign matter, 
as plaster of Paris, porcelain, base metal, amalgam, etc. 
These substances should be removed and the waste 
then reduced to ashes, using no fluxes. Mix the residual 
matter with about one-quarter its weight of saltpeter 
(powdered). Place the mixture in a red hot clay cru- 
cible (the crucible should not be more than half full), 
and cover with a thin layer of salt to. prevent froth- 
ing. Keep the crucible at a very high heat until the 
slag is thin enough to allow the metal to settle. This 
is determined by plunging an iron rod into the cruci- 
ble. When removed the slag should run freely from 
the rod. In case, however, the slag refuses to become 
thin, add more saltpeter and a little borax, and in- 
crease the heat if possible. Finally, remove the 
crucible from the furnace, tap it gently on some 



APPLIED TO DENTISTRY. 125 

solid object, let it cool undisturbed, then break it 
open and remove the metal, which should be collected 
in the form of a button in the bottom, if the work has 
been conducted properly. In case the metal is 
bright and malleable it may be treated at once 
by Method III. If, however, the button is dull and 
brittle, it still contains some base metal. Hammer or 
roll out the button, cut in small pieces, place in a 
clean clay crucible and "saltpeter," as indicated in 
Method I., until clean. Finally, refine by Method III. 

METHOD I. 

Select a clean clay crucible and heat it in the fur- 
nace until red hot. Introduce the fragments of- gold 
to be remelted, and add a small quantity of saltpeter 
(crystals). Replace the furnace cover, and so regu- 
late the heat that the gold will melt as quickly as 
possible. In the meantime clean the interior of the 
upright ingot mold (Fig. 19) with a cloth, and then 
oil it. Common machine oil will answer the purpose, 
but do not use inflammable oils. Place the mold on 
top of the furnace to warm. The oil protects the 
gold from contamination with iron and the heat pre- 
vents the molten metal from cooling too rapidly and 
thus forming an ill-shaped ingot. When the gold is 
melted and ready to pour, place the mold in a con- 
venient position, remove the crucible by means of the 
crucible tongs (Fig. 12), and pour the metal not too 
rapidly into the mold. Immediately remove the in- 
got and wash it, using for this purpose soap and a 
stiff scrub-brush. Next anneal by holding it in a 
flame, or by placing it in the furnace. When a cherry 
red color is reached plunge it into a dilute solution of 



126 CHEMISTR Y AND ME TALL URGY 

sulphuric acid and again wash, dry, and proceed to 
roll it out (see page 111), reannealing at times during 
the operation. Should it happen that the ingot is brit- 
tle and refuses to roll without cracking cut it in small 
pieces, place the pieces in a clay crucible and subject 
to the highest temperature of the furnace. When 
molten, raise the crucible to the top of the furnace by 
means of the tongs; throw small crystals of saltpeter 
into the metal, and give the crucible a gentle circular 
motion to insure thorough mixing. Continue the heat 
for some time, and finally again pour into the upright 
mold. If the ingot still persists in cracking, repeat 
the operation just described. 

METHOD II.* 

When the larger scraps have been cut in small 
pieces, place them together with the filings, etc., in a 
flat bottom flask, designed to withstand heat, and 
cover with aqua regia. In making the acid use two 
parts of concentrated hydrochloric to one part of con- 
centrated nitric acid. Place the flask on a sand bath, 
apply heat gently and at times add small portions of 
acid to maintain the reaction. It may happen that 
some fragments of gold become coated with a film 
of silver chloride and refuse to be acted upon 
by the acid. In such a case decant the acid liquid, 
rinse the flask with a little water and boil the 
fragments with ammonium hydroxide until the 

*This method, if carefully followed, will yield practically 
chemically pure gold. 



APPLIED TO DENTISTRY. 127 

film of silver chloride is removed. Carefully decant 
the liquid, replace the acid and continue applying 
the heat until the gold is completely dissolved. 
Silver present in the original substance remains as a 
residue in the bottom of the flask. Remove this by 
filtration, but before doing so add enough water to 
weaken the acid somewhat. Wash the last trace 
of the yellow gold solution from the filter paper. 
The residue on the filter is silver chloride and may 
be reduced to silver by fusing on charcoal with 
sodium carbonate. The gold chloride solution should 
now be transferred to a large beaker or jar and 
diluted with water until only faintly acid in taste. 
Prepare a clear solution of ferrous sulphate, roughly 
calculating that five parts of the sulphate crystals are 
required to precipitate one part of gold. Add this 
slowly to the gold solution and allow the resulting 
brown precipitate of metallic gold several hours in 
which to settle. When the supernatant liquid has 
become clear add a little more ferrous sulphate to 
insure complete precipitation. Decant the clear 
liquid and boil the gold with dilute hydrochloric 
acid to remove iron. Pour the acid on a filter and 
continue boiling with fresh portions of acid until sat- 
isfied that all traces of iron are removed. Finally^ 
transfer the gold to the filter and wash with hot water 
until no acid is detected in the washings. Dry in an 
air bath or in a porcelain dish over a burner; incin- 
erate the paper and fuse the metal with the addition 
of a little borax and saltpeter on charcoal with a 
blowpipe (Fig. 23), or in a clay crucible in the fur- 



128 CHEMISTR Y AND MET ALL URGY 

nace. Gold, carefully prepared as indicated, is pure 
and should be very soft and malleable. Should it 
be found brittle, however, likely due to imperfect 
washing, "saltpeter " it as indicated in Method I. 

METHOD III. 

Method Lis designed to remove base metals only. 
Although Method II. separates every metal from the 
gold, it is a tedious operation and need seldom be 
employed except in cases where platinum is present in 
the scrap in considerable quantity. The method 
about to be described, commonly called quartation, 
is very convenient and rapid and is applicable in 
cases where silver, copper, and indeed small quan- 
tities of platinum are to be removed from clean scrap. 
The gold to be refined is fused with three times its 
weight of copper or clean scrap silver, on charcoal, 
if small in quantity, otherwise in a clay crucible. The 
alloy obtained is next hammered or rolled out, cut in 
small pieces and subjected to the action of strong 
nitric acid (commercial) until entirely disintegrated. 
When this point is reached, water is added to weaken 
the acid somewhat, so that it will not attack the 
filter and the residue of metallic gold is separated 
from this solution by filtration, care being exercised 
to wash with hot water until no acid is*detected in 
the washings.* Both paper and gold should next be 
dried and treated as already indicated in Method II. 
Gold thus prepared is usually 996-998 fine. 

*In case silver has been used to alloy the gold, save the 
filtrate and the washings, and recover the silver as indicated on 
page 130. 



APPLIED TO DENTISTRY. 129 

Refining Silver. 

The problem here presented involves the prepara- 
tion of pure silver for use in making amalgam-alloys, 
etc., from the following classes of scrap. 

Class I "Standard" scrap and other commercial 
alloys rarely containing, besides silver, a wider range 
of metals than copper and zinc. This class of scrap 
can be treated directly as indicated below. 

Class II. Waste dental amalgam containing silver, 
tin, mercury and at times gold, platinum, zinc, cop- 
per, etc. First, separate the mercury as follows: 
Place the amalgam in an iron retort (Fig. 22), and ap- 
ply sufficient heat to distill the mercury, which sub- 
sequently should be purified as shown on page 131. 
Remove the residue from the retort and refine as 
indicated below. 

The recovery of silver from any alloy containing an 
abundance of tin is somewhat troublesome owing to 
the fact that after digesting the alloy in nitric acid, tin 
is converted into an insoluble residue which clogs a 
filter paper and prevents the silver solution from run- 
ning through. These facts must be borne in mind in 
refining this class of waste, and instead of attempting 
to remove any bulky residue by filtration it should be 
allowed to settle and the clear liquid decanted or 
siphoned off. Finally, the residue should be thrown 
upon two folds of loose muslin attached to a wood 
frame and washed free from silver, i. e., until the 
washings give but a faint opalescence with hydro- 
chloric acid or salt. 



130 CHEMISTRY AND METALLURGY 

METHOD. 

Place the metal in a flask, and cover with nitric 
acid. Apply heat to the flask placed on the sand 
bath, and at times add small quantities of acid to 
maintain the reaction. This operation should be 
carried on in a good draft or in a hood to 
carry off disagreeable fumes. When action finally 
ceases, dilute the acid somewhat with water, sepa- 
rate any insoluble residue and add to the clear 
liquid sufficient common salt solution to completely 
precipitate the silver as silver chloride. Stir vigor- 
ously, warm and let settle. Decant the clear liquid, 
and pass in water from a faucet in such a manner 
as to thoroughly agitate the precipitate. Repeat 
this operation two or three times, and finally transfer 
the precipitate to a wet filter and wash until acid is 
no longer detected in the washings. Remove the 
precipitate and paper from the funnel and dry, as in 
the case of gold, but do not try to incinerate the 
paper. Place paper and precipitate in a graphite 
crucible and cover with sodium carbonate or charcoal 
and potassium carbonate. Reduce the silver chloride 
to metallic silver in the furnace and pour into a 
clean bullion mold (Fig. 18), or granulate by pouring 
into water. Silver carefully prepared as indicated is 
pure enough for all ordinary purposes. 
Refining Mercury. 

The mercury to be refined may contain : 

/. Mechanical impurities, as dust, etc. Refine as 
indicated in Method I. 



APPLIED TO DENTISTRY. 131 

//. Metallic impurities, as those retained when 
mercury is squeezed or distilled from amalgams.* 
Remove the bulk of the impurities by redistillation 
or by Method I., and finally refine by Method II. or 
III. 

METHOD I. 

Make a pin hole in blotting paper or in a rough 
filter paper placed in a funnel and filter the mercury. 
Much of the impurities will be left on the paper. 
This treatment, followed by washing, will usually be 
found sufficient to remove mechanical impurities. 

METHOD II. 

Place the mercury in a shallow dish and cover its 
surface with very dilute nitric acid. Agitate fre- 
quently during several hours The acid will dissolve 
the impurities together with a little mercury. 
Finally wash the surface of the mercury under a 
stream of water from the faucet, dry with a clean 
sponge or blotting paper then on a water bath or over 
a low flame, 

METHOD III. 

Place the mercury in a dry bottle and cover its 
surface with finely powdered sugar. The mercury 
should occupy but one-fourth the capacity of the 
bottle. Shake the bottle vigorously, removing the 
cork at times to admit a fresh supply of air. The 
foreign metals are oxidized and cling to the grains of 

*A portion of the foreign metals usually passes over with the 
mercury as vapor or as the result of spirting. 



132 CHEMISTR Y AND ME TALL URGY 

sugar. Filter as indicated in Method I., wash and 
dry. Pure mercury does not tarnish, has no film on 
its surface after standing, and does not leave a " tail " 
when made to run down a slight incline. 



APPLIED TO DENTISTRY. 133 



CHAPTER XIII. 



DENTAL AMALGAMS AND AMALGAM=ALLOYS. 

Certain alloys, commonly known as dental 
amalgams, are employed for filling cavities in 
decayed teeth. From the broad definition of the term 
given in Chapter X., it would follow that any metal- 
lic compound containing mercury is an amalgam. In 
dentistry, however, the expression is used in a 
restricted sense, having reference only to the product 
resulting from the admixture by direct contact of a 
finely divided metal or alloy with sufficient mercury 
to form a plastic mass. As just stated, amalgams 
are sometimes made by amalgamating a single metal. 
Thus precipitated copper (see p. 31), when tritu- 
rated in a mortar with dilute mercuric nitrate and 
mercury, yields the so-called copper amalgam, the 
use of which is now practically discontinued. In 
most cases, however, amalgams for fillings are made 
from alloys composed chiefly of silver and tin, and 
commonly called amalgam-alloys. By combining these 
metals in varying proportions it is possible to pro- 
duce alloys which yield more satisfactory amalgams 
for dental purposes than does a single metal, such as 
silver or copper or any combination of other metals. 
Silver-tin amalgams, however, possess certain objec- 



134 CHEMISTR Y AND ME TALL URGY 

tionable features, and for the purpose of counteract- 
ing these, small quantities of some other metal or 
metals are often introduced. The metals usually 
added for this purpose are gold, copper, platinum, 
zinc, and occasionally aluminum and cadmium. As 
a rule, the proportion of silver and tin entering into 
these alloys varies from sixty-five per cent of silver 
and thirty-five per cent of tin to forty per cent of sil- 
ver and- sixty per cent of tin. . In certain cases, 
however, as high as seventy-four per cent of silver is 
added. The composition of many of the well-known 
amalgam-alloys can be seen by referring to the 
Appendix, Section II. 

After being melted these alloys are cast in an ingot 
mold and are then reduced to a fine state, either by 
filing them or by cutting them in a lathe. In this con- 
dition they are intimately mixed with mercury by 
kneading in the palm of the hand or in a small mortar 
until a homogeneous, coherent mass has been formed. 
An amalgam which probably possesses definite chem- 
ical composition in many cases now exists dissolved 
in an excess of mercury, and to use it as a filling 
material it is necessary to remove the excess. Usu- 
ally this is accomplished by wringing through chamois 
skin with the aid of pliers. The mercury passes 
through the pores of the straining material, leaving a 
plastic, crystalline mass, which emits a peculiar crack- 
ling when pressed, probably due to the grating of the 
crystals upon each other. In this state the amalgam is 
packed in the cavity of the tooth,where, in a short time, 
it loses its plasticity and forms a hard, metallic plug. 



APPLIED TO DENTISTRY. 135 

Properties of Amalgams. 

Amalgams possess many peculiar properties, and 
under certain conditions undergo changes which re- 
quire special consideration. 

COLOR AND LUSTER. 

Amalgams are uniformly white or gray, even when 
gold or copper is present in large quantities. After 
hardening they are capable of taking a high silver-like 
polish and of retaining it, as well as their color, 
indefinitely in the absence of tarnishing substances. 
When placed in the cavity of the tooth, however, they 
sooner or later lose their brilliancy and discolor 
superficially. These changes, which are due chiefly 
to the influence of hydrogen sulphide resulting from 
the decomposition of certain foods in the mouth and 
somewhat to the action of drugs and vegetable acids, 
constitute an objection to amalgams as a filling mate- 
rial. Moreover, the sulphides and other compounds 
formed often permeate the tooth substance and greatly 
discolor it, a fact which is particularly noticeable in 
the case of silver-tin amalgams containing copper and 
those containing cadmium. Accordingto manyauthor- 
ities, however, the substances formed, particularly in 
the case of silver and copper, exert a preservative 
influence upon the tooth. 

Although the discoloration of amalgams cannot 
be prevented entirely, it can be controlled somewhat 
by eliminating copper from the formula of an amal- 
gam-alloy and by adding 3 small proportion of gold 
or of zinc. 



136 CHEMISTRY AND METALLURGY 

SOLIDIFICATION. 

After an amalgam has been mixed it begins to 
lose its plasticity and in a comparatively short time 
it reaches a state of hardness in which it can no 
longer be worked. In dentistry this change is called 
"setting." It must not be inferred, however, that an 
amalgam has reached its hardest state just after solidi- 
fication has occurred. Indeed, it is generally recog- 
nized that the process of hardening continues for 
hours or even for days. 

Amalgams differ greatly in the time required for 
solidification. Tin amalgams and those prepared 
from amalgam-alloys containing a high percentage of 
tin set slowly and imperfectly, while those amalgams 
formed from amalgam-alloys containing a large pro- 
portion of silver set very quickly and become very 
hard. The quickest setting are those prepared from 
alloys containing seventy to seventy-five per cent of 
silver. 

Metals which tend to hasten setting when added 
in certain proportions to a silver-tin alloy are gold, 
platinum, copper, zinc and cadmium. Concerning 
the effects of the two first named metals, there seems 
to be considerable controversy. It is generally recog- 
nized, however, that the addition of platinum to a 
silver-tin alloy containing gold induces the property 
of setting quickly. 

The proportion of mercury in an amalgam is a 
factor asregards solidification. An amalgam contain- 
ing an excess of mercury will set more slowly than the 
same amalgam with the excess of mercury removed. 



APPLIED TO DENTISTRY. 137 

Finally, the treatment to which an amalgam-alloy has 
been subjected after cutting and before amalgamating 
greatly affects the setting properties of the amalgam. 
A freshly cut alloy will yield a much more rapidly set- 
ting amalgam than will an " aged" or " annealed" sam- 
ple of the same alloy, i. e., an alloy which in the form of 
filings or shavings has been exposed for a long time to 
the action of the air or has been heated for a short time 
at the temperature of boiling water. 

CHANGE OF VOLUME. 

At the time of the change from the plastic to the 
hard state and in some instances after hardening ap- 
parently has taken place, amalgams undergo a change 
of volume which in magnitude, in the time required 
for its completion, and in the manner in which it pro- 
ceeds differs widely in different alloys and in different 
conditions of the same alloy. With most amalgams the 
change is so slight that it requires a delicate microm- 
eter to detect it; in a few instances, however, it can 
be easily observed by the naked eye. In some cases it 
continues for a short time and then ceases; in others, it 
proceeds for hours or days and sometimes for weeks. 
Finally, it may result either in expansion or contrac- 
tion. It does not always happen, however, that the 
final volume is the result of an increase or decrease 
alone. Indeed, it is quite common for an amalgam to 
expand for some time and then to contract or vice versa. 
Silver-tin alloys containing less than fifty per cent of 
silver produce amalgams which shrink at first and 
then expand. Those containing over seventy-five 
per cent of silver yield amalgams which expand only. 



138 CHEMISTRY AND METALLURGY 

This tendency to change in volurtie constitutes the 
greatest objection to amalgams as filling material. 
An amalgam which contracts will draw away from 
the wall of the cavity and allow the ingress of mois- 
ture, i. e., "leakage." Those which expand will often 
assume a convex form on the surface when packed in 
a cavity and produce the phenomenon commonly 
termed "spheroiding." This tendency to "spheroid" 
is undoubtedly the result of expansion in the direction 
of least resistance and is similar to the phenomenon 
observed when water freezes in a vessel. 

According to the researches of G. V. Black, 
expansion and contraction are influenced by the com- 
position of the amalgam-alloy. 

Of the silver-tin alloys, those containing sixty-five 
per cent of silver and thirty-five per cent of tin are 
said to yield amalgams which show the least expan- 
sion or contraction when used freshly cut. 

An alloy containing seventy-three per cent of silver 
and twenty-seven per cent of tin produces, when 
fully annealed, an amalgam which shows no change 
of volume. Those metals which, when added in 
small proportions, are said to decrease the tendency 
to contract are gold and copper. According to the 
experiments of Dr. Black, zinc induces an expansion 
which continues for an indefinite time. A great 
diversity of opinion still exists as regards the effects 
upon amalgams of many of the metals commonly 
added in small quantities to amalgam-alloys. 

The chemistry underlying this change of volume 
cannot be explained. It is interesting to note, how- 



APPLIED TO DENTISTRY. 139 

ever, that in one case, at least, it is the direct result 
of the oxidation of one of the constituents of the 
amalgam-alloy. A silver-tin alloy containing as little 
as one or two per cent of aluminum expands 
greatly and becomes hot when amalgamated in the 
hand. When the mass is placed under the micro- 
scope bubbles of gas are seen to escape. The expla- 
nation of these phenomena (deduced from experiments 
made by the author) is as follows: The aluminum 
amalgam in the presence of moisture decomposes the 
water, the aluminum being oxidized and the hydrogen 
of the water being set free. The hydrogen — some of 
which is seen to escape — being liberated within the 
mass naturally brings about a change analogous to 
that produced by carbon dioxide in raising bread. 
This explanation is substantiated by the fact that 
if the amalgam is made in a perfectly dry mortar 
comparatively little expansion takes place. If, how- 
ever, a drop of water is added, the mass almost 
instantly increases to three or four times its original 
volume. 

STRENGTH AND CHANGE OF FORM WITH PRESSURE. 

A solid amalgam presents a peculiar combination 
of properties which seldom is observed in any one 
substance. Thus, if an amalgam is struck a sudden 
blow with a hammer, it will fly in pieces; but if the 
force applied is comparatively light it will yield 
greatly before breaking. In many instances it is pos- 
sible to reduce an amalgam to a thin sheet. This 
tendency to yield to pressure is, in dentistry, com- 



HO CHEMISTRY AND METALLURGY 

monly called " flow;" and the amount of pressure 
which an amalgam will sustain without breaking is 
taken as representing its strength. The flow of 
amalgams differs, however, in a certain respect from 
that of the metals. For example, a block of silver, 
steel, iron or gold when subjected to pressure yields 
suddenly and then ceases unless the pressure is 
increased. With a block of amalgam under like con- 
ditions a different phenomenon is observed : "When 
the flow has begun it continues as long as the stress 
is maintained. No increase of the stress is required 
to maintain the flow even after the area of the amal- 
gam has been greatly increased by the flattening of 
the mass between plane surfaces. If a stress of fifty 
pounds be put upon a block of amalgam and main- 
tained for one hour, flow will occur at a certain rate; 
if the stress be reduced to twenty-five pounds the 
flow will continue, but at a reduced rate." "It will go 
slowly with a light stress, somewhat quicker with a 
heavier stress, but it cannot be made to go very 
quickly with a very heavy stress; it will break into 
fragments."* 

The flow of an amalgam is generally regarded as 
of greater importance than the crushing-strength, 
since many amalgams which are capable of with- 
standing the crushing force of mastication will 
gradually yield, and thus their adaptation to the 
margins will be destroyed. An increase of tin in a 
silver-tin alloy increases the flow and decreases the 

*G. V. Black, Dental Cosmos, Vol. XXXVII. , p. 558, 



APPLIED TO DENTISTRY. 141 

strength. The addition of but small proportions 
of gold to a silver- tin alloy greatly increases the 
flow and reduces the strength. With copper, the 
opposite is noted. Obviously the manner of mixing 
and packing, the time given for hardening, etc., have 
an influence upon the flow and strength of an amal- 
gam, and for this reason the results of measurements 
of these properties on the same amalgam are not 
liable to be very constant. 

SOLUBILITY. 

Most amalgams are but slightly soluble in the 
fluids of the mouth, except when the saliva is strongly 
acid or alkaline and when other metals, such as gold 
and aluminum, are present. Under these conditions 
galvanic action is induced, and this greatly facilitates 
their solution. From the strong galvanic action often 
detected in the mouth, it would seem probable that 
the lack of permanence of fillings which is com- 
monly attributed to the flow and to the expansion and 
contraction of amalgams is due in part to this 
agency. The chief objection to the use of copper 
amalgams is that they disintegrate under the action 
of the fluids of the mouth. 

Preparing and Testing Amalgam-Alloys and 
Amalgams.* 

It will be the object here not only to teach the 
mechanical manipulation involved in making these 

*A convenient form of record to be kept by the student in 
performing these exercises is shown in the Appendix, Section II. 



142 CHEMIST R Y AND ME TALL URGY 

alloys, but also to offer some opportunity to observe 
their physical properties. Since this can best be 
accomplished by laboratory exercises, the student is 
directed to prepare about twenty-five grams of amal- 
gam-alloy according to a formula to be assigned by 
the instructor, and to amalgamate it and to study and 
test the resulting amalgam as described later. In 
doing this work the metals may be used which have 
been refined as directed in Chapter XII. 

The general directions to be followed and precau- 
tions to be observed in making alloys have already 
been given in Chapter X., and are applicable here to 
a certain extent. The preparation of amalgam-alloys, 
however, involves certain operations not described 
elsewhere in this book, and in order that the student 
may have a detailed outline to follow in preparing 
these special alloys, the complete process is described. 
The various steps consist in: 

1. Weighing the metals. 

2. Melting and pouring. 

3. Comminuting. 

4. Sifting and removing particles of iron. 

5. Annealing. 

i. Weighing the Metals. First, calculate from the 
formula of the alloy the quantity of each metal needed 
to make the required quantity of alloy, and then pro- 
ceed to weigh out the metals, using for this purpose 
the balance illustrated in Fig. 4. For convenience 
in handling the metal should be in the form of small 
pieces. Silver can be purchased in the granulated 
and tin in the shot form, 



APPLIED TO DENTISTRY. 143 

2. Melting and Pouring. Select a clean graphite 
or clay crucible and add the silver, covering its sur- 
face with borax. Place the crucible in the furnace 
and heat until the silver melts and sinks below the 
surface of the molten borax. Without removing the 
crucible from the furnace introduce the tin (also gold 
and copper). When the content of the crucible is 
in a molten state, stir carefully once or twice with a 
pine stick (do not use an iron rod, as is often directed). 
When satisfied that the metals are thoroughly alloyed 
remove the crucible from the furnace, give it a gentle 
circular motion with the tongs and pour the alloy 
as quickly as possible into a clean mold (Fig. 18).. 
When zinc or cadmium is to be added, introduce 
it with constant stirring after removing the crucible 
from the furnace. 

j. Comminuting. Amalgam- alloys are converted 
into a fine state either by filing them or by cutting 
them in a lathe. For filing an alloy the so-called 
bastard file, about fourteen inches in length, is best 
suited. When alloys are to be converted into shavings 
in a lathe they should be cast in a mold which 
furnishes a rod-shaped ingot. An alloy containing a 
large percentage of tin will be found to cut easily and 
to give coarse filings. Such alloys have a tendency 
to clog the file and hinder its action. In case this hap- 
pens clean it with a steel brush. Alloys rich in silver 
give fine filings, and hence the character of the fil- 
ings is often taken as indicating the approximate 
composition of the alloy. 

4. Sifting and Removing Particles of Iron. When 



144 CHEMISTR Y AND ME TALL UR G Y 

an alloy has been filed, it should be sifted through a 
sieve of forty, sixty or eighty meshes, depending upon 
the character of the filings, to remove pieces of alloy 
which have been broken from the ingot. 

After sifting, an ordinary magnet should be 
passed through the filings in order to remove 
particles of iron which have been broken from the file. 

5. Annealing. Attention has already been called 
to the fact that filings which have been cut for some 
time or have been heated possess certain properties 
not shown by those freshly cut. This peculiar 
change, which undoubtedly is due in part at least to 
a superficial oxidation of the tin since in the alloyed 
state this metal is very susceptible to oxidation, is 
looked upon as conferring desirable properties upon 
the mass when amalgamated. There is considerable 
controversy concerning the chemistry of annealing, 
some insisting that it is a molecular change. What- 
ever importance may be attached to this theory, it 
nevertheless is true that in many respects the theory 
of superficial oxidation is consistent with the facts 
observed. 

To anneal an alloy, place the filings in a test tube 
or flask and keep the vessel in boiling water for fif- 
teen minutes. This time is usually sufficient, 
although in some cases in order to obtain the desired 
results it may be necessary to heat for a longer time. 
It is a noticeable fact that when annealing is carried 
too far the amalgam sets slowly and is reduced 
in strength. Thus, if an alloy is heated a minute or 
so in the naked flame at a temperature somewhat 



APPLIED TO DENTISTRY. 145 

above boiling water, it will turn brown, due to the 
oxidation of the tin, and will produce an amalgam 
which is practically worthless. Annealed alloys take 
up much less mercury than freshly cut and yield a 
greater quantity of the so-called " dirt," upon mixing. 
This black substance is a lower oxide of tin. 

MIXING AMALGAMS. 

The amalgamation of filings or of shavings is usu- 
ally effected by rubbing them with mercury in the 
palm of the hand, in a small mortar or in both. In all 
cases the mixing should be thorough and the mercury 
used should be pure. The quantity of mercury to be 
employed necessarily varies with different alloys and 
with the different conditions of the same alloy. 
Freshly cut alloys require much more mercury than 
those which have been annealed, and fine filings take 
up more mercury than those which are coarse. The 
proportions usually range, however, from two parts 
of alloy and one of mercury to equal parts of each. 

It is often urged that in mixing amalgams the pro- 
portion in which the mercury and the alloy combine 
be determined by experiment and that thereafter 
they be weighed out accurately in that proportion. 
This method is seldom followed in practice. In all 
cases, however, if the constituents are not weighed 
care should be taken to avoid a great excess of mer- 
cury. The chief reason for this arises from the fact 
that in expressing the excess of mercury from an 
amalgam more or less tin is removed, and thus the 
composition of the amalgam-alloy is changed. To 



146 CHE MIS TR Y AND ME TALL URGY 

what extent comparatively large proportions of mer- 
cury may affect the composition of an amalgam-alloy 
can be seen by briefly reviewing some results 
obtained by the author. A silver-tin alloy of the com- 
position, silver sixty-five, tin thirty-five, was made 
and a certain weight of this alloy in the form of filings 
was mixed with an equal weight of mercury. The 
excess was removed by squeezing through heavy 
muslin, and the expressed mercury was analyzed. In 
no case was more than a trace of the silver in the 
amalgam-alloy removed. With the annealed alloy 
1.7 per cent of the tin was removed, and with the 
freshly cut 0.86 per cent was removed. A second 
series of experiments in which the same weight 
of alloy as above and twice the weight of mercury 
was used, gave surprisingly different results. Under 
these conditions 4.38 per cent of tin was removed 
from the annealed and 4.18 per cent from the freshly 
cut alloy. A third series of experiments in which the 
alloy and mercury were mixed in the proportion of 
one part of the former to five parts of the latter 
showed that 9.6 per cent of the tin was removed from 
the annealed and 9.8 per cent from the freshly cut 
alloy. An interesting fact developed by these experi- 
ments was that in all the determinations made, about 
twenty-five in number, the tin constituted almost 
exactly one per cent of the mercury removed. 

In removing the excess of mercury from an amal- 
gam, chamois skin or good muslin may be used. Ob- 
viously the pressure exerted in wringing will determine 
theproportion of mercury left in the amalgam, which in 



APPLIED TO DENTISTRY. 147 

all cases should be the least that will suffice to make 
a mass which can be manipulated. Certain devices 
are suggested for amalgamating by shaking. The 
objection to using these, however, will become appar- 
ent if some alloy and mercury are shaken in a test 
tube. The result will be that the black substance 
commonly observed in mixing amalgams, i. e., the 
lower oxide of tin, will separate in large quantities. 
Thus it is seen that the danger of changing the com- 
position of the amalgam-alloy by this method of mix- 
ing is very great. Indeed, it is possible by continued 
shaking as described to remove a large proportion of 
the tin from an amalgam. 

TESTING AMALGAM-ALLOYS AND AMALGAMS. 

With the ingot of amalgam-alloy which has been 
prepared the following exercise may be performed 
before it is converted into filings: 

i. Determination of Specific Gravity. By means of 
a hack-saw cut the ingot into three pieces of about 
equal size and mark each by a scratch with a file. 
Next weigh each portion of the ingot on the ana- 
lytical balance and record the results as weight in air. 
Then place a small bench, which is to be found in 
the drawer of the balance case, astride the left-hand 
scale pan in such a manner as to allow the pan to 
swing freely below it. In this place a 200 c. c. beaker 
two-thirds filled with distilled water at about 15° C. 
Next tie a piece of linen thread about eight inches 
long to one of these ingots and suspend it from a 
hook on the stirrup, carrying the left-hand scale pan, 



148 CHEMISTRY AND METALLURGY 

in such a manner that the ingot is completely im- 
mersed in the water in the beaker. By means of a 
fine brush remove any bubbles of air that may cling 
to the ingot, and then counterpoise it by placing the 
required weights on the right-hand scale pan. Record 
the result as the weight in water. With the weight 
in air and in water known, the specific gravity of the 
portion of the ingot in question can be determined by 
the following formula: 

Weight in air _ 

- TT . . — : . TTT . . — = =Specinc gravity. 

Weight in air — Weight in water 

In this manner the specific gravity of all three 
portions should be determined and compared. In 
case the ingot is homogeneous these values should 
agree very closely. If, however, from any reason the 
metals have not been properly combined, more or 
less variation will be observed. After these facts 
have been noted, the average of the three results 
may be compared with the specific gravity calculated 
from the proportions of the metals employed in pre- 
paring the alloy. In this way the change in specific 
gravity accompanying alloying may be noted: 

The three portions of the ingot may now be con- 
verted into filings which may be employed for the 
following tests: 

2. Test for Discoloration. Amalgamate about two 
grams of the alloy, roll it into a ball and place it in a 
test tube. Fill the tube with distilled water, saturate 
with hydrogen sulphide gas, and cork the tube. After 
twenty-four or forty-eight hours the color of this sam- 



APPLIED TO DENTISTRY. 149 

pie may be compared with that of some freshly mixed 
amalgam. In this way the tendency of different amal- 
gams to discolor can be roughly determined. 

j. Tests for Change of Volume, Before making 
these tests anneal about one-half of the amalgam-alloy 
which has been prepared and place the annealed 
sample in a labeled bottle. 

I. Weigh out accurately two grams of the freshly 
cut alloy on the analytical balance. Remove 
the weights from the scale pan, place a gram 
weight on the pan with the alloy and exactly coun- 
terpoise the alloy and gram weight with mercury. 
This gives two grams of alloy and three grams 
of mercury. Transfer both the alloy and the mer- 
cury from the scale pan to a rubber cot. Amal- 
gamate thoroughly, squeeze out the excess of mer- 
cury, carefully collect this on a sheet of filter 
paper and retain it in a labeled test tube for use in 
Special Tests given later. Pack the amalgam in one of 
the cavities in the steel block* (Fig. 29) with filling 
instruments. Dress the surface of the filling level 
with the face of the block (do not burnish) and take 
particular care so to adapt it to the margins of the 
cavity that when viewed under the microscope no 
openings are observed. 

II. In the manner just described prepare a sam- 



*Before making these tests it will be necessary for the student 
to burnish the faces of the steel block, and carefully to smooth 
the margins of the cavities so that they show no irregularities 
under the microscope. 



150 CHEMISTRY AlSfD METALLURGY 

pie of amalgam from the annealed alloy, weighing 
the constituents, amalgamating and retaining the 
expressed mercury in a second labeled test tube. 
Pack the resulting mass of amalgam in the second 
cavity of the steel block, following the directions 
given above. 

III. Finally prepare a third sample of amalgam 
as follows : Weigh out as directed two grams of the 
freshly cut alloy and three grams of mercury. Place 
the alloy in a dry test tube or porcelain crucible and 
subject it to a low heat over a Bunsen flame until 
somewhat oxidized, i. e., until it turns brown. 
Amalgamate this, retain the expressed mercury in a 
third labeled test tube and pack the mass in the third 
cavity of the steel block. 

When the fillings have been completed, the steel 
block may be placed in the micrometer and the change 
of volume measured from time to time as directed on 
page 116. Microscopical examinations of the margins 
of the fillings should accompany the micrometrical 
measurements. In all this work the student should 
observe the general working properties of the differ- 
ent samples of amalgam, particular attention being 
directed to their setting properties. 

4. Tests for Strength and Flow. Prepare two cubes 
of amalgam from the freshly cut alloy by packing them 
in the matrix. (Fig. 31.) When they have been 
given five days in which to harden determine their 
strength and flow in the dynamometer as described on 
page 118. Prepare and test in the same manner 
cubes of amalgam made from the annealed and 



APPLIED TO DENTISTRY. 151 

from some oxidized alloy and note the effects of 
annealing and oxidizing upon strength and flow. 

5. Special Tests. In the study of amalgams it is 
essential that some tests be made to show the differ- 
ent quantities of mercury taken up by equal weights 
of the same amalgam alloy in the freshly cut, in the 
annealed and in the oxidized states, and to determine 
the proportions of tin* removed in squeezing out the 
excess of mercury. In making these determinations the 
mercury which was retained in tl*e labeled test tubes 
from the Tests for Change of Volume may be used. 

I. To determine the different quantities of mer- 
cury taken up under the conditions stated above: 
Weigh the contents of each test tube. Since three 
grams of mercury were employed in each case, the 
mercury retained by each amalgam is equal to the 
difference between this weight and that of the ex- 
pressed mercury. f Retain the three samples of expressed 
mercury for tests given below. 

Problem 1. Knowing the formula of the amalgam- 
alloy, the weight of amalgam-alloy taken (2 grams) 
and the quantity of mercury in each amalgam, calcu- 
late the percentage composition of the three amal- 
gams which were tested for change of volume. 

^Although a very small quantity of silver may be removed in 
the mercury expressed from a silver-tin alloy, it would be imprac- 
ticable for the student to attempt to estimate it. Whether such 
metals as zinc and aluminum are removed, if present in the 
amalgam-alloy, has not been definitely determined. 

fThis result, of course, will not be exactly correct, since the 
weight, owing to the presence of more or less tin, does not repre- 
sent pure mercury. 



152 CHEMISTRY AND METALLURGY 

II. To determine the quantities of tin removed 
from the amalgam-alloy by the three samples of 
expressed mercury proceed with each as follows: Care- 
fully transfer the mercury from the test tube to a 200 
c. c. beaker (the beaker should be labeled); add about 
10 c. c. of concentrated nitric acid and an equal volume 
of distilled water; warm gently over a hot-plate. The 
mercury dissolves and the tin, if present, remains as 
a white residue, Sn0 2 . When the mercury is dis- 
solved, boil the contents of the beaker gently for five 
minutes, then add 25 c. c. of distilled water and filter 
through a quantitative filter paper.* Wash the residue 
on the paper until no acid can be detected in the wash- 
ings. Reject both the filtrate and washings and allow 
the paper and residue to dry in an air bath. When 
dry, wrap the paper containing the residue into a 
small bundle and place it in a porcelain crucible 
(Fig. 26) the weight of which should have been deter- 
mined previously- Place the crucible on a pipestem 
triangle (Fig. 21) and apply the flame of the Bunsen 
burner until the paper is completely burned and the 
residue is white. Allow the crucible to cool and then 
weigh. Subtract the weight of the crucible from the 
combined weight of the crucible and the residue and 
the result is the weight of the residue, which is tin 
oxide, Sn0 2 . Multiply this by the factor 0.788 and 
the result is the weight of metallic tin removed by x 
grams of mercury. 

*A special land of paper used in quantitative analysis which 
gives practically no ash when incinerated. 



APPLIED TO DENTISTRY. 153 

Problem 2. Determine what percentage of the x 
grams of expressed mercury is tin. 

Problem 3. Determine what percentage the tin 
removed is of the total weight of tin in the two 
grams of amalgam-alloy taken. 

After completing the various tests outlined above 
the student should test in the*same manner the amal- 
gams made from one or more of the prominent amal- 
gam-alloys found upon the market. 

Copper Amalgam.* 

Owing to the fact that copper amalgam has practi- 
cally gone out of use in dentistry, it is but briefly con- 
sidered here. To prepare a small quantity as a labo- 
ratory exercise the student may proceed as follows : 
Weigh out roughly twenty-five grams of pure copper 
sulphate crystals and dissolve, with the aid of heat, in 
250 c. c. of distilled water. When the crystals 
are dissolved acidify the solution with sulphuric 
acid and immerse in it a rod of iron or of zinc. 
The precipitation of red metallic copper begins at 
once and continues until it is removed from the 
solution, i. e., until the blue color of the solution has 
disappeared. The bar of iron or of zinc is freed from 
adhering copper, then removed; the clear supernatant 
liquid is poured off; the residue of copper is washed 
by decantation several times with hot water containing 

*For more facts concerning copper amalgam than are given 
in this book, the student is referred to Flagg's ' 'Plastics and Plastic 
Filling" and to the article by G. V. Black in the Dental Cosmos, 
Vol. XXXVII., p. 737. 



154 CHEMISTRY AND METALLURGY 

a little sulphuric acid, and finally with cold water 
until no acid is detected in the last washings. The 
copper is next transferred to a mortar and moistened 
with a solution of mercuric nitrate, which forms a 
coating of mercury on it. About twelve or thir- 
teen grams of mercury are then added and rubbed 
with the copper until amalgamation is completed. 
The mass of amalgam is next washed with water and 
squeezed in chamois skin or muslin. Again it is 
rubbed in the mortar, squeezed in chamois skin 
and finally made into pellets and allowed to harden. 

When required for use a pellet is placed upon a 
spatula and heated over a flame until the /'beads" of 
mercury appear on the surface. The heating must not 
be carried to-o far, for this will oxidize the copper* It is 
then crushed in a mortar until plastic, in which con- 
dition it is ready for use. 

According to the tests of G. V. Black, copper 
amalgam retains its margins well, changes in volume 
but slightly and furnishes a very rigid filling material. 
These tests further show that copper amalgam is 
reduced in strength by frequent reheating, and hence 
the residue amalgam should not be used. 



APPLIED TO DENTISTR\ . 155 



CHAPTER XIV. 



THE ASSAY OF AMALGAM=ALLOYS.* 

By the application of certain chemical methods it 
is possible to. determine accurately the proportions of 
the constituents present in a complex substance such 
as an alloy. This is known as quantitative chemical 
analysis as distinguished from qualitative which, as 
has already been shown, f serves only to separate and 
identify the constituents without determining their 
quantity. Quantitative analysis may be divided into 
gravimetric and volumetric. In gravimetric analysis 
the substance is usually precipitated in some insoluble 
form much as in qualitative and then carefully filtered, 
dried and weighed. The process followed in volu- 
metric analysis consists in estimating the substance 
by measuring accurately the volume of a reagent of 
known content, commonly called a standard solution, 
necessary to bring about a certain complete reaction. 
The determination of tin and zinc as outlined here- 
after is an example of gravimetric analysis, while the 
estimation of copper by means of a solution of potas- 
sium cyanide illustrates volumetric. 

The quantitative analysis of many amalgam- 

*The form of the report to be submitted upon the completion 
of this work is shown in the Appendix, Section II. 

tSee Chapter IX. 



156 • CHEMISTRY AND METALLURGY 

alloys is not difficult and some knowledge of simple 
methods may at times be a matter of importance to the 
dentist. To determine successfully the composition of 
alloys containing a greater variety of metals than 
silver, tin, copper, zinc and gold requires an exten- 
sive knowledge of analytical chemistry and hence 
is not touched upon here. 

The student may apply the methods outlined here- 
after to the assay of a sample of the alloy used in the 
work upon amalgams, and in so doing he can deter- 
mine how nearly it is possible to realize in the ingot 
the proportions of the metals placed in the crucible. 
The general scheme of separation is given in the 
accompanying table and the details* of manipulation 
are explained under the different methods. 

Method I. 

ESTIMATION OF TIN. 

The residue remaining on the filter after dissolv- 
ing the sample in nitric acid consists of the tin as 
oxide, SnO s , and the gold. If the latter is present 
it will cause the precipitate to be purple in color. 
When gold is present it is weighed with the tin oxide 
and from the weight of the two the amount of gold 
found by the Fire Assay (Method IV.) is deducted and 
the tin oxide equals the difference. 

Place the dried precipitate in a weighed porcelain 
crucible and ignite gently at first, then at the highest 
heat of the Bunsen burner. Cool and weigh. The 
weight of SnO s multiplied by 0.788 equals the 
amount of tin present. This multiplied by 100 gives 
the percentage of tin in the alloy. 



APPLIED TO DENTISTRY. 



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158 CHE MIS TR Y AND ME TALL URG Y 

Method II. 

ESTIMATION OF COPPER. 

The estimation of copper may be accurately and 
quickly made by the so-called volumetric cyanide 
method. It requires a solution of potassium cyanide, 
the equivalent of which in copper is carefully deter- 
mined.* 

Dissolve the precipitate of copper sulphide on the 
paper with hot nitric acid and wash the paper with 
hot water, collecting the washings in the beaker with 
the nitric acid solution. If the sulphur residue on 
the paper is dark colored then wash all the contents 
of the filter into the nitric acid solution and boil. 
Filter and wash. Cool the filtrate, add a slight 
excess of ammonium hydroxide and then add 
the potassium cyanide from a burette (Fig. 35) to 
the copper solution in a beaker until the blue color 
disappears. Multiply the number of cubic centimeters 
of cyanide solution used by the weight of copper to 
which 1 c. c. of the cyanide solution is equivalent, 
then multiply the product by 100, which gives the per- 
centage of copper in the alloy. 

Method HI. 

ESTIMATION OF ZINC. 

Dilute the filtrate, which may contain zinc, to 
about 400 c. c, and heat it to boiling. Now remove the 
beaker from the hot-plate, cover with a watch crystal, 

*For directions for preparing and standardizing this solution 
see Appendix, Section I. 



APPLIED TO DENTISTRY. 159 

and add from the end of a spatula, a little at a time, 
sodium carbonate, replacing the watch crystal after 
each addition to prevent loss by spirting. Continue the 
addition of the sodium carbonate until the zinc is all 
precipitated and the sodium carbonate is in excess, 
which may be ascertained by a piece of litmus paper. 
Now place the beaker on the hot-plate, heat it to 
boiling, stirring at intervals to prevent bumping. 
Boil hard for about fifteen minutes. Remove the 
beaker from the hot-plate and let it stand until the 
precipitate is completely settled. Decant the super- 
natant liquid onto a quantitative filter, and to the pre- 
cipitate add about 100 c. c. of hot water and stir 
thoroughly. Allow to settle and again decant the 
clear supernatant liquid. Repeat the washing by 
decantation about five times, then wash the precipi- 
tate onto a filter and continue washing the precipitate 
with hot water until the wash water shows no alkaline 
reaction with red litmus paper. Allow the filter to drain, 
then transfer both precipitate and paper to a weighed 
porcelain crucible. Ignite very cautiously at first to 
avoid spirting. This may best be done by playing 
the flame on the crucible until the precipitate is dry. 
Finally heat at a high temperature until the paper is 
burned and the residue is light yellow in color. Cool 
and weigh. Weight of zinc oxide, ZnO, multiplied 
by 0.803 gives the weight of zinc, and this result mul- 
tiplied by 100 gives the percentage of zinc in the 
alloy. 



160 CHE MIS TR Y AND ME TALL URGY 

Method IV. 

FIRE ASSAY FOR GOLD AND SILVER. 

The assay of alloys for gold and silver by ordinary 
gravimetric or volumetric methods is not as quick nor 
as accurate as the fire methods, and this is particularly 
true in alloys containing much tin or copper. 

The fire assay consists in melting the alloy in 
twenty to forty times its weight of granulated lead 
contained in a scorifier (Fig. 13) together with a small 
quantity of borax glass. The latter being a strong flux 
unites with the base metals to form a slag or glass 
which is essentially borates of lead and of other base 
metals. But as the amount of borax used is small 
there necessarily will be but a small slag which at first 
appears as a glassy ring in the outer edge of the 
molten metals. If a current of air is allowed to pass 
over the hot lead (and other metals) it is oxidized 
and passes off as fumes of lead oxide. If now the heat 
be continued the amount of lead will keep decreasing 
and the ring of slag will appear to become larger; but 
in reality it is only " closing in" as the mass of lead 
becomes smaller from volatilization. On heating 
long enough, which usually is from thirty to forty 
minutes, the slag will close in and cover the whole 
surface of the lead, leaving but a small button hidden 
from view in the bottom of the scorifier. As gold 
and silver do not form compounds with the borax, 
but have a strong affinity for the hot lead, the button 
will contain all the gold and silver with possibly small 
amounts of copper or tin, 



APPLIED TO DENTISTRY. 161 

On cooling and separating the slag from the but- 
ton the next operation is to separate the gold and 
silver from the lead. This is done by again melting 
the lead, this time in a cupel (Fig. 15), allowing a cur- 
rent of air to pass over it. The red hot lead is con- 
verted into lead oxide, which is partly absorbed by 
the cupel and partly volatilized. The operation is con- 
tinued until finally all the lead, with traces of copper 
and tin, are driven off or absorbed and nothing remains 
but the bright bead of gold and silver. 

The bead is then weighed, the silver dissolved by 
nitric acid and the insoluble gold again weighed. 
This subtracted from the total weight of gold and 
silver gives the weight of silver. 

From the foregoing it will be seen that the assay 
really consists of several operations which are fol- 
lowed in regular order : 

1. Weighing sample and preparing charge. 

2. Scorification. 

3. Cupellation. 

4. Weighing gold and silver bead. 

5. Parting. 

6. Weighing and calculating. 

/. Weighing Sample and Preparing Charge. Two 
assay tons (60 grams) of granulated lead are weighed 
out on the pulp balance and about one-half is placed 
in a scorifier. Before doing this, however, chalk 
the inside of the scorifier. This prevents the hot lead 
from attacking it and eating a hole through it. 
Now weigh out accurately on the analytical balance 
one gram of the sample alloy and carefully brush 



162 CHE MIS TR Y AND ME TALL URGY 

on top of the granulated lead in the scorifier, then add 
the balance of the lead. On top place a small pinch 
of borax glass equal to about one gram. 

2. Scorification, Place scorifier and contents in the 
back part of the muffle, close the latter with the plug 
and increase the heat. When the lead is melted and 
the ring of slag is formed, draw the scorifier to the 
center of the muffle and allow the air to enter. The 
plug is not replaced unless the muffle should get too 
cool. It will now be noticed that the fumes of lead 
oxide are continually forming on the surface of the 
lead and passing off up the chimney. The heat is 
continued until the ring of slag gradually closes in 
and in from thirty to forty minutes completely covers 
the hot lead. Now replace the plug and heat strongly 
for about five minutes. Then remove the scorifier 
and pour the contents into a button mold (Fig. 17). 
It is a good plan to warm the mold before pouring. 
This may be done by placing it on the top of the muffle 
furnace during the operation of scorification. When 
cold, the slag and button are emptied from the mold 
and the button is hammered to free it from slag. It 
is usually hammered into a cube. The button should 
be malleable and not crack. If it does show a tend- 
ency to crack it may be due to copper or some other 
base metal. In such cases it is best to rescorify with 
about a ton and a half of lead and a pinch of borax 
glass. 

j. Cupellation. Select a cupel of about twice the 
weight of the button and place it in the hot part of 
the muffle for a few moments. Next carefully place the 



APPLIED TO DENTISTRY. 163 

button in the cupel and close the muffle with the plug. 
If the cupel and muffle are quite hot the lead will 
melt at once and the surface will be seen to brighten 
and fumes of lead will begin to come off. The cupel 
is now carefully drawn forward and the heat so regu- 
lated that the "scales" or " feathers" of crystallized 
lead oxide appear on the inside of the cupel. It is 
difficult to describe the proper heat that is required, 
but it may be said that it is about right when the 
"feather" forms. It is essential that the heat in cupel- 
ling be carefully watched. The reason for this is that 
silver is appreciably volatile at high temperature. 
On the other hand, the temperature must not be so 
low as to allow the cupel to " freeze " and oxidation 
to stop. Should the latter occur a piece of charcoal 
placed against the cupel will usually heat it suffi- 
ciently to again start oxidation. Whenever freezing 
occurs, however, the results are usually doubtful. 

When the lead has disappeared by absorption 
and by volatilization and the bead of gold and silver 
appears, replace the plug, remove the cupel to the 
back of the muffle and heat for about five minutes to 
drive off the last trace of lead. Then turn off the 
heat, remove the plug and gradually draw the cupel to 
the front of the muffle to cool. Do not cool too sud- 
denly or the bead will "sprout," and possibly occa- 
sion a loss. The next step is to weigh the gold and 
silver bead. 

4. Weighing the Gold and Silver Bead. Carry the 
cool cupel containing the bead to the balance and with 
a pair of pinchers pick up the bead. Tighten the 



164 CHE MIS TR Y AND ME TALL URGY 

pinchers, and with a stiff brush clean the bead, 
then place it in the pan of the balance and weigh. 
Record the weight as total gold and silver. The 
next operation is to separate or "part" the gold and 
silver. 

5. Parting. Pure silver is readily dissolved in 
nitric acid, but if gold be alloyed with it in consider- 
able proportion its solubility is decreased so that to 
completely separate gold and silver by this means it is 
essential that they be in the proportion of about two 
parts of silver to one of gold. But as silver is always 
present in amalgam-alloys in very much larger pro- 
portions than gold it will not be necessary to " in- 
quart." After weighing, place the bead on a clean 
anvil, and with a small hammer flatten it. If the bead 
is hard and not malleable it may be due to the 
presence of some other metal. This must be 
removed by wrapping in about five grams of pure 
sheet lead and again cupelling and weighing. Often 
the bead may be rendered more malleable by heating 
to a dull red heat on charcoal with a blowpipe for a 
few moments. But if the brittleness be due to the 
presence of a foreign metal it will be necessary to 
recupel or the result will be too high in silver. 

Place the flattened bead in a porcelain crucible 
and fill half full of nitric acid, sp. gr. 1.2. Boil on a 
hot-plate, keeping the crucible covered with a watch 
crystal. After it has boiled for several minutes and 
the brown fumes have passed off remove from the 
hot-plate and cool. Then with the aid of a glass rod 
pour off the bulk of the acid and fill the crucible half 



APPLIED TO DENTISTRY, 165 

full of nitric acid, sp. gr. 1.3, and again boil for a few 
moments to dissolve the last trace of silver. The gold 
will now be found in the bottom of the crucible as 
fine black particles, contaminated with some silver 
nitrate in solution. The latter is removed by washing 
withdistilled water. This is done by filling the crucible 
with water, tapping gently to cause the particles of gold 
to settle and then pouring off the water, using a glass 
rod. Again add water, repeating the operation four 
or five times. Finally drain the crucible as much as 
possible, and then soak up the last drop of water 
with a bit of filter paper, but be very careful that the 
paper does not touch any particles of gold. Wipe the 
crucible dry with the paper and complete the drying 
by placing it on the warm part of the hot-plate. Next 
transfer to a triangle and heat for a few moments at 
a red heat, which will bring out the yellow color. If 
no gold is present the first acid treatment will dis- 
solve the silver to a clear solution. But no matter 
how small the black, insoluble gold may be, an attempt 
should be made to weigh it. If, however, it can be 
seen but cannot be weighed on a sensitive balance 
it is then usually called a " trace." 

6. Weighing and Calculating. When the crucible 
is cool enough to handle, it is taken to the bal- 
ance and the gold transferred to the balance pan by 
the aid of a needle point and weighed. This weight 
gives the gold. Multiply by 100 to convert into per- 
centage. Subtract the weight of gold from the total 
weight of gold and silver and the difference equals the 
silver. Multiply this by 100 to obtain the percentage 



1 66 CHEMISTR Y AND ME TALL URGY 

of silver in the alloy. In case gold is found in the 
alloy its weight should be subtracted from the. 
weight of tin oxide obtained under Method I. This 
result multiplied by the factor 0.788, and then by 100 
gives the percentage of tin. 



APPLIED TO DENTISTRY. 167 



CHAPTER XV. 



SOLDERS AND SOLDERING. 

Solders are alloys used to join metallic surfaces. 
As a rule they consist of the metal upon which they 
are to be used alloyed with some other metal or 
metals capable of considerably lowering the melting 
point without greatly modifying other physical 
properties. When dissimilar metals are to be united, 
a solder should be used which possesses an affinity 
for both and corresponds as nearly as possible to them 
in color, hardness, malleability, etc. In all cases 
solders should flow readily. In addition, it is obvious 
that solders for dental purposes should discolor but 
slightly and should be capable of resisting the action 
of the fluids of the mouth. 

At times it is necessary to unite metals without 
the use of solders. This is accomplished by a process 
known as autogenous soldering, which consists in fusing 
together the contiguous parts. This method of solder- 
ing is extensively employed in plumbing and in the 
manufacture of various apparatus for chemical indus- 
tries. Thus lead chambers used in the manufacture 
of sulphuric acid are soldered autogenously, since a 
common soft soldercontaining tin would soon corrode. 
By using the oxyhydrogen blowpipe it is possible 



168 CHEMISTR Y AND ME TALL URGY 

to solder platinum vessels for chemical purposes in 
this manner where a solder of even gold, with which 
platinum usually is soldered, could not be used to 
advantage. 

Many kinds of solders, known by the names of 
tin, alui?iinum, copper, brass, argent an, silver, gold, 
jewelers', plui?ibers\ etc., are used in the arts. 
Although the names just given are commonly em- 
ployed in distinguishing one solder from another, all 
may be broadly classified as hard or soft. Hard 
solders comprise those which fuse at or above red 
heat, and hence are used on metals possessing high 
melting points, while soft solders include those which 
fuse easily, and are used particularly by plumbers and 
tinsmiths, on metals fusing at low temperatures. 

Preparation of Solders. 

In preparing solders few directions are necessary 
beyond those already given for making other alloys. 
When zinc is to be added to a solder it should be intro- 
duced after the other constituents are melted and after 
the temperature has been reduced somewhat, other- 
wise it will be partially or even wholly oxidized. 
When both copper and zinc are to be added to a solder 
it is advisable to use instead of the separate metals, 
the proper quantity of pure brass, since in this state 
the zinc is less liable to be oxidized. 

Soft solders are commonly used in the stick form; 
hard solders are often cast into ingots and converted 
into filings; gold and silver solders are usually rolled 
into sheets and used in the form of clippings. 



APPLIED TO DENTISTRY 



169 



As a laboratory exercise* in solder making, the 
student may prepare such quantities of aluminum, 
silver and gold solders as he may require for use in 
other departments of work. 

SOFT SOLDERS, 

Tin Solders. Tin solders are used chiefly in sol- 
dering tin plate, copper and Britannia metal. In den- 
tistry they are sometimes employed in making appli- 
ances for regulating teeth. The best solder of this 
class consists of tin, two parts, and lead, one part; 
the common variety is composed of tin, one and one- 
half parts, and lead, one part. The various tin sol- 
ders and the temperatures at which they melt are given 
in the following table ; 





Parts. 






Parts. 




No. 




Melting 


No. 




Melting 
















Point. 








Point. 




Tin. 


Lead. 






Tin. 


Lead. 




1 


1 


25 


292° C. 


7 


Wz 




168° C. 


2 


1 


10 


283° C. 


8 


2 




171° C. 


3 


1 


5 


266° C. 


9 


3 




180° C. 


4 


1 


3 


250° C. 


10 


4 




185° C. 


5 


1 


2 


2-i:° c. 


11 


5 




192° C. 


6 


1 


1 


188° C. 


12 


6 




194° C. 



In preparing tin solders, melt the tin first and then 
add the lead; stir vigorously and pour into a cold 
mold. The melting should be done in a crucible in- 

*For the form of report to be made upon this work see 
Appendix, Section II. 



170 



CHEMISTRY AND METALLURGY 



stead of an iron ladle, as a little iron absorbed by the 
solder would greatly increase its melting point. 

Chemical Solder. Pure tin in the form of foil is 
often used in soldering small articles. The pieces 
are fitted together with the foil between them and 
then held in the flame of a Bunsen burner until 
joined. In this manner an invisible joint can be 
made if the soldering is conducted carefully. 

Bismuth Solders. The so-called bismuth solders, 
which properly may be classed with the fusible 
alloys described later, are composed of bismuth, lead 
and tin, and melt at temperatures ranging from 95° C. 
to 160° C. They are very fluid when melted and con- 
siderably harder than common solders. Although 
very satisfactory they are too expensive for general 
use owing to the content of bismuth. The formulae 
of some bismuth solders are given below : 





Parts. 




No. 








Melting 




Tin. 


Lead. 


Bismuth. 


Point. 


1 


3 


5 


3 


94.4° C. 


2 


2 


2 


1 


109.4° C. 


3 


2 


1 


2 


113.3° C. 


4 


1 


1 


1 


123.3° C. 


5 


3 


3 


1 


154.4° C. 


6 


4 


4 


1 


1G0.0°C. 



Aluminujfi Solders. For dental and other pur- 
poses aluminum possesses many advantages over 
other metals, and hence the soldering of it is a matter 



APPLIED TO DENTISTRY. 171 

of great importance; but, although many solders 
and methods of soldering have been proposed, few if 
any of them have proved to be entirely successful. 
The obstacles encountered in soldering aluminum are 
many. It melts at a comparatively low temperature, 
and hence can be soldered only with an alloy possess- 
ing a low melting point. But to obtain a solder which 
will melt easily and at the same time produce a strong 
joint is a difficult matter. It must be composed 
chiefly of the more fusible metals, such as tin, zinc, 
lead, etc. These, however, form weak solders which 
seem unable to "wet" the aluminum, and hence to 
attach themselves firmly to the surfaces to be united. 
Again, for dental purposes a solder must be employed 
which will retain its color and will not dissolve in the 
fluids of the mouth. Finally, a flux must be em- 
ployed which will clean and protect from oxidation 
both the metal and the solder without attacking 
either. Common fluxes, as borax, cannot be used for 
this purpose since they exert an injurious influence 
upon aluminum and prevent union. 

The solders given below are suggested by Schlosser 
as particularly adapted to soldering dental work, 
since they resist the action of corrosive substances. 

PLATINUM-ALUMINUM SOLDER. GOLD-ALUMINUM SOLDER. 

Gold 3 parts. Gold 5 parts. 

Platinum 0.1 ■■ Copper 1 H 

Silver 2 M Silver 1 ■■ 

Aluminum .10 " Aluminum 2 " 

When silver chloride is fused on aluminum it is 
reduced and the silver forms an alloy on the surface 



172 CHEMISTR Y AND ME TALL URG Y 

of the aluminum. These facts are taken advantage of 
for soldering aluminum. The fused, finely powdered 
silver chloride is used as a flux with ordinary solders. 
It is placed at the junction and the soldering com- 
pleted with the brazing blowpipe. 

A solder recommended by Richards consists of : 

Tin 29 parts. 

Zinc 11 

Aluminum 1 V 

Phosphor tin (tin containing phosphorus)l ' ' 

This solder fuses easily and may be applied with 
a copper or nickel soldering iron. The edges to 
be soldered are scraped clean and then tinned 
either by heating and rubbing them with the solder 
or by applying the solder to them with a soldering 
iron. When this is done the soldering can be com- 
pleted in any desired manner without flux. 

A solder which has proved very satisfactory for 
general use in the dental laboratory is that prepared 
by the author's students. It consists of: 

Aluminum 45 parts. 

Tin 45 

Mercury 10 M 

This solder may be applied by aid of a brazing 
blowpipe and a piece of steel wire. 

Although there may be solders and methods of 
soldering more satisfactory than those given, it should 
be remembered that it is a difficult matter to learn 
much about them, as they are held in great secrecy by 
those employing them. 



APPLIED TO DENTISTRY. 



173 



HARD SOLDERS. 

Brass Solders. Brass solders are sometimes used 
in place of soft or silver solders, for soldering brass, 
copper, etc. They consist of copper, zinc and some- 
times tin. As the content of tin increases, the color 
of the brass becomes lighter and its ductility is dimin- 
ished. Brass solders containing no tin are yellow, 
while those alloyed with this metal are known as 
half wliite and white, as shown below. In the follow- 
ing table are given the proportions of brass, tin and 
zinc used in making some common brass solders: 



Golden yellow (refractory). 
Half white (readily fusible) 
White 



BRASS. 


ZINC. 


3 


1 


12 


5 


20 


1 



TIN. 



In making these solders a good quality of sheet 
brass is used. Fuse the brass, then add the zinc and 
tin and stir thoroughly. Remove the crucible from 
the furnace as soon as the metals are thoroughly 
mixed. 

Brass solders are commonly used in the granu- 
lated form. The granulation may be effected by 
pouring the melted alloy through a wet broom. 

Silver Solders. Silver solders, which consist of 
silver alloyed with certain proportions of copper, 
zinc and often tin, have a broad application. They 
can be used in soldering articles of silver, brass, 



174 CHEMISTRY AND METALLURGY 

German silver, cast iron, steel, etc. The small pro- 
portion of tin sometimes added renders the solder 
more fusible and causes it to flow more easily. 

The following formulae are often recommended 
for general use: 

no. 1. 

Pure silver 8 parts. 

' * copper , 1 " 

" zinc 2 M 

Another solder may be made of : 

no. 2. 

Pure silver 2 parts. 

Brass wire 1 " 

A hard silver solder for soldering articles which 
are to be hammered or stamped, may be made as 
follows: 

no. 3. 

Silver 4 parts. * 

Copper 1 

A solder for steel may be made of: 

no. 4. 

Silver 3 parts.* 

Copper 1 " 

In preparing silver solder from the separate metals, 
melt the silver under considerable borax, add. the 
copper and finally introduce the zinc as usual. In 
case brass is used instead of copper and zinc sepa- 
rately, add it after the silver has melted. 

*Brannt's " Metallic Alloys." 



APPLIED TO DENTISTRY. 175 

Silver coin may be used instead of pure silver in 
preparing solders. The silver coin of the United States 
is composed of silver, ninety parts, and copper, ten 
parts. 

Silver solder is commonly used in the form of 
clippings; hence, pour the metal into the upright ingot 
mold (Fig. 10) and roll the ingot, as described on 
page 111, into a plate of 26 or 28 gauge. 

Gold Solders. These are alloys used in uniting 
articles composed of pure or alloyed gold. Besides 
gold, they contain copper, silver, and often some 
zinc. As several standards of gold are used by den- 
tists and jewelers, solders of different degrees of fine- 
ness, usually ranging from 12 to 20 carats, are used. 

Obviously, in order to obtain the most artistic, as 
well as the most substantial results, the color of the 
solder should correspond to that of the material upon 
which it is to be used, and its melting point should 
be but slightly lower. As stated above, zinc is some- 
times added to gold solders. It reduces the melt- 
ing point and improves the flow, but is objectionable, 
especially if in excess, owing to the fact that it ren- 
ders the solder brittle and difficult to roll, and at times 
oxidizes to such an extent that it leaves the surface 
"pitted." 

The following formulae are suggested for making 
satisfactory solders for dental purposes. As gold coin 
is often employed in making gold solders, the pro- 
portions of this alloy, as well as those of pure gold to 
be used, are given. 



176 



CHEMISTR Y AND ME TALL URGY 



NO. 1. 12-CARAT GOLD SOLDER. 



Gold 12 parts. 

Silver 6 

Brass..... 6 



Gold coin (U. S.). . 13.3 parts. 

Silver 6 

Brass.. 4.7 '« 



NO. 2. 13-CARAT GOLD SOLDER. 

Gold 13 parts, j Gold coin (U. S.). . 14.4 parts. 

Silver 6 ■• Silver 6 

Brass 5 •■ | Brass 3.6 " 

NO. 3. 15-CARAT GOLD SOLDER. 



Gold 15 parts. 

Silver 4 " 

Brass 5 '• 



Gold coin (U. S.). . 16.6 parts. 

Silver 4 

Brass 3.4 •■ 



NO. 4. 16-CARAT GOLD SOLDER. 



Gold 6 parts. 

Silver 2 " 

Brass 1 " 



Gold coin (U.S.)... 6.6parts. 

Silver 2 

Brass 0.4 " 



NO. 



5. 18-CARAT GOLD SOLDER. 



Gold 27 parts. 

Silver 4 " 

Copper . 2.5 M 

Brass 2.5 " 



Gold coin (U. S.). ... 30 parts. 

Silver 4 " 

Copper M 

Brass 2 " 



The following solders are recommended for crown and bridge 
work : 

NO. 6. 20-CARAT GOLD SOLDERS.* 

Gold 20 parts. 

Silver 2 ■« 

Copper 1 

Spelter solder (Cul, Znl) 1 

low's solder. Richmond's solder. 

Gold coin (U. S.) 12 parts. Gold coin (U. S..) 5 parts. 

Silver 2 " Brass wire 1 " 

Copper 1 " 

The method of preparing gold solder does not 
differ from that given for making silver and other 



*Essig's "American Text-book of Prosthetic Dentistry." 



APPLIED TO DENTISTRY. 177 

solders. Only pure metals should be used; care 
should be taken to insure thorough mixing, and 
finally, the mold into which the solder is to be poured 
should be scrupulously clean. Gold solders should 
be cast in the upright ingot mold and rolled in the 
same manner as silver solders. 

Solders for Aluminum Bronze. The difficulties 
encountered in soldering aluminum are not met with 
in soldering aluminum bronze. The following solders 
are recommended for ten per cent aluminum bronze:* 

NO. 1. HARD SOLDER. NO. 2. MEDIUM HARD SOLDER. 

Gold 88.88 Gold 54.40 

Silver 4.68 Silver 27.60 

Copper 6.44 Copper 18.00 

NO. 3. SOFT SOLDER. 

Bronze (Cu 70, Sn 30) 14.30 

Gold 14.30 

Silver 57.10 

Copper...' 14.30 

Platinum Solder. As already stated, platinum for 
chemical purposes is soldered autogenously. For 
other purposes, however, pure gold is used. Owing 
to the difficulty with which it is melted, soldering 
with pure gold requires great skill in order to obtain 
perfect joints. 

Soldering. 

In applying soft solders the soldering iron is 
commonly used. This consists of a pointed piece of 
copper called the bit, attached by an iron stem to 

* Richards' "Aluminum. ". 



178 CHEM1STR V AND ME TALL URGY 

a wooden handle. In order to solder successfully, 
the bit should be kept clean and tinned on the point. 
This can be done by heating it in a Bunsen burner, or 
preferably in a bed of charcoal, then rubbing in 
ammonium chloride (sal ammoniac) and finally in 
some soft solder. 

In applying hard solders either a mouth or brazing 
blowpipe (Fig. 23) is used, as the highest temperature 
of the soldering iron is not sufficient to melt the solder. 

In soldering, the following rules should be observed: 

1. The surfaces to be united should be fitted 
together closely and, if necessary, held in position by 
binding-wire or in some other manner. 

2. The surfaces should be scrupulously clean, 
i. e., free from oxides, grease, etc.- This is often accom- 
plished by scraping or polishing them, but more often 
by applying dilute acids as sulphuric or hydrochloric. 

3. Some means should be adopted to prevent the 
air from coming in contact with the heated surfaces. 
This is especially necessary in hard soldering. For 
this purpose fluxes are used. In soft soldering the 
so-called soldering fluids are employed. They are 
designed to clean and to protect the surfaces and 
at the same time to cause the solder to flow. A satis- 
factory flux of this sort can be made by saturating 
commercial hydrochloric acid with zinc. Instead of 
this fluid common rosin can often be used. For hard 
soldering borax is the most common flux. It not 
only prevents oxidation but also removes oxides from 
the metals. It is best applied in the form of a thin 
paste made by mixing pulverized borax with water. 



APPLIED TO DENTISTRY. 179 

4. The quantity of both solder and flux should be 
the least that will suffice. An excess of either is very 
objectionable, especially in hard soldering. 

5. In hard soldering the temperature should be 
raised gradually and care should be taken not to over- 
heat. When large surfaces are being soldered it is 
customary to carefully heat the entire piece uniformly 
before directing the flame upon the parts to be united. 

6. An oxidizing flame should be avoided, as it 
oxidizes the base metals and thus interferes with the 
operation. 

7. After soldering, the joint should not be dis- 
turbed until the solder has thoroughly hardened. 



180 CHEMISTRY AND METALLURGY 



CHAPTER XVL 



MISCELLANEOUS ALLOYS. 

In this chapter various alloys, some of which have 
important applications in dentistry, are considered. 
Since it would be impracticable for the student to 
attempt to prepare all of even the more important 
alloys described herein, it may be well to indicate 
that the preparation and study of fusible alloys offers 
an interesting and instructive laboratory exercise. 
Therefore, about twenty-five grams each of two of the 
more important representatives of this class, prefer- 
ably Mellotte's and Wood's, may be made, and their 
physical properties, particularly their low melting 
point, noted.* 

Fusible Alloys. 

As already stated, the term fusible alloy is applied 
to a number of metallic compounds, composed chiefly 
of tin, lead, bismuth, and occasionally cadmium and 
mercury, which melt at very low temperatures, in some 
instances even below the temperature of boiling water. 
In most cases, especially if the proportion of bis- 
muth is high, the alloy is brittle and considerably 
harder than any of the metals composing it. 

*The form of report to be submitted upon the completion of 
these exercises is shown in the Appendix, Section II. 



APPLIED TO DENTISTRY. 181 

In the dental laboratory fusible alloys are used for 
crown and bridge work and for various other pur- 
poses. One of the most common alloys of this class 
is that introduced by Mellotte. It has the following 
composition : * 

Bismuth 8 parts. 

Tin 5 M 

Lead 3 »« 

This alloy melts at about 100° C. and expands on 
solidifying. It is harder than tin, somewhat softer 
than zinc and quite brittle. In order to obtain impres- 
sions to be used with it, a compound of potter's clay 
and glycerine, called "moldine," is used. This sub- 
stance, although retaining its plasticity for a long 
time, eventually becomes hard and has to be made 
plastic again by moistening with glycerine. Another 
fusible alloy, suggested by C. M. Richmond for dental 
uses, has the following composition : 

Tin 20 parts. 

Lead 19 '• 

Cadmium 13 »■ 

Bismuth 48 •• 

This alloy is said to be as hard as zinc. It melts 
at about 65.5° C. 

In addition to the alloys given above a table of 
others, some of which are often employed in dentistry, 
is given below. 

*Essig's "American Text-book of Prosthetic Dentistry." 



182 



CHEMISTRY AND METALLURGY 



Fusible Alloys. 



Name. 



Hodgen's . 
Darcet's . . 
Rose's. .. 
Newton's.. 
Onion's. . . 
Wood's. . . 
Lipowitz's 
Darcet's . . 
(with mercury) 















ji 






6 


>> 


p 


-4-> 






p 


u 







B 


d 


T3 
03 


6 


u 
93 


a 

c 


PQ 


H 


J 


o 


§ 


<< 


8 
4 
2 
8 
5 
4 
15 
2 


3 
1 
1 
3 
2 
1 
4 
1 


5 
3 
1 
5 
3 
2 
8 
1 






2 
























1 

3 










10 





W) . 

12 



105° 
96° 
95° 
94° 
92° 
65° 
63° 
45° 



In preparing these alloys mix the constituents 
excepting the cadmium and mercury, and melt 
them under charcoal. As the tendency of lead 
to separate is very great, stir the alloy thoroughly with 
a pine stick before pouring. Cadmium and mercury 
should be added after the other metals are melted, 
otherwise they will be volatilized. 

DETERMINATION OF MELTING POINT. 

To determine the melting point of a fusible alloy, 
proceed as follows : Select a clean, thin-walled test 
tube and bind to it by means of rubber bands a ther- 
mometer in such a manner that the bulb of the 
thermometer lies against the bottom. of the tube. 
Place the alloy to be tested in the tube and immerse 
the tube and its contents, with the thermometer 
attached, in a beaker of distilled water. The water 
is then heated, with constant agitation, over a hot- 



APPLIED TO DENTISTRY. 183 

plate until the alloy melts. The source of heat is 
withdrawn and the temperature at which the alloy 
solidifies is noted. The mean temperature of two or 
three of these observations is taken as the melting 
point of the alloy. Obviously water can be used only 
where the alloy fuses below 100° C. When the alloy 
to be tested melts at or slightly above this tempera- 
ture some ammonium chloride or common salt may be 
added to the water to raise its boiling point, or a 
liquid possessing a higher boiling point than water, 
such as glycerine or sulphuric acid, may be used. 
For the determination of the melting point of an 
alloy which melts considerably above the tempera- 
ture of boiling water other methods must be employed 
which cannot be described here. 

Alloys for Dies. 

An alloy which is to be employed in making dies 
should possess the following properties: It should 
not be so brittle that it will break under the blows of 
a heavy hammer; it should shrink but slightly upon 
solidifying; it should fuse at a comparatively low 
temperature; and finally, it should flow easily in order 
to make a perfect reproduction of the model. 

Pure zinc seems to meet most of the requirements 
called for above, and hence it is widely used for making 
dental dies. Although it contracts somewhat in the 
act of cooling, this is said by some to be immaterial 
since it serves to counteract the expansion which the 
plaster model undergoes in setting. 

Crude zinc cannot be used for making dental dies 



184 CHEMISTR Y AND ME TALL URGY 

owing to the impurities in it which render it very 
brittle and greatly impair certain other physical prop- 
erties. A variety which is highly recommended for 
dental uses is that known as Bertha zinc* 

Babbitt Metal, This alloy is made according to a 
great many formulae. A compound of the following 
composition is recommended by Haskell for dental 
purposes: 

Copper 1 part. 

Antimony 2 " 

Tin 8 " 

This alloy is said to be nearly as hard as zinc, and 
to contract less. Common Babbitt will not do for dies. 

In preparing Babbitt metal, melt the copper 
and half of the tin, then add the antimony and the 
remainder of the tin. Stir vigorously and keep the 
surface of the alloy covered with powdered charcoal. 
Babbitt metal deteriorates when melted repeatedly. 

Spence's "Metal." This is a compound occasionally 
used in making dies. It is not strictly an alloy, but 
a solution of the sulphides of metals, as lead, iron, 
antimony, zinc, etc., in melted sulphur. For dental 
purposes the compound made by melting iron sul- 
phide in sulphur is commonly used. It melts at 160° 
C. and expands on cooling. It gives very good cast- 
ings. 

Type Metal. Type metal,, which is used in the 
manufacture of type and frequently in dentistry for 
making dies, varies considerably in composition. A 
good variety is composed of: 

*Essig's "American Text-book of Prosthetic Dentistry." 



APPLIED TO DENTISTRY. 185 

Lead 4 parts. 

Antimony 1 " 

Tin 1 " 

It is brittle, harder than lead, softer and more 
fusible than zinc, and is capable of giving accurate 
castings. 

In making type metal melt the lead first, then add 
the tin, and finally the antimony. Carefully regulate 
the temperature of the furnace in order not to oxidize 
the antimony. Keep the alloy covered with charcoal. 

Alloys of Zinc and % Tin. An alloy suggested by 
Richardson for making dies and described as being 
harder and more fusible than zinc is composed of 
zinc, four parts, and tin, one part. Similar alloys are 
frequently employed in casting patterns and orna- 
ments. 

Alloy for Counterdies. 

The alloy commonly employed for counterdies 
with Babbitt metal dies consists of lead, seven parts, 
and tin, one part. 

Gold Plate. 

For dental purposes gold plate of 18 or 20 carats is 
commonly used. A lower carat than 18 is not desirable 
since it discolors readily and is more or less acted 
upon by the saliva ; a higher carat than 20 lacks 
rigidity to withstand the strain of mastication when 
used for artificial dentures. When it is required, how- 
ever, to employ higher grades of gold plate they are 
usually alloyed with small quantities of platinum, and 



186 CHEMISTRY AND METALLURGY 

this renders them very rigid. The formulae of several 
varieties of gold plate are given below. 

18-CARAT GOLD PLATE. 



Pure gold 18 parts. 

Copper 2 " 

Silver 4 " 



Gold coin (U. S.) 20 parts. 

Copper ■« 

Silver 4 '*■ 



20-CARAT GOLD PLATE. 



Pure gold 20 parts. 

Copper 1.5 ,< 

Silver . 2.5 »■ 



Gold coin (U.S.) 22 parts. 

Copper 4 ' 

Silver 2 " 



22-CARAT GOLD PLATE. 

Pure gold 22 parts. 

Copper 0.25 " 

Silver 1.50 " 

Platinum 0.25 M 

18-CARAT GOLD PLATE FOR CLASPS, HARD WIRE, ETC. 



Pure gold 18 parts. 

Copper 3 M 

Silver 2.25 " 

Platinum 0.75 »' 



Gold coin (U. S.) 20 parts. 

Copper 1 

Silver 2.25 " 

Platinum 0.75 M 



In the preparation of gold plate no directions 
beyond those already outlined for the preparation of 
gold solders need be given. The alloy should be 
poured into the clean, warm, upright ingot mold. 
After annealing it is rolled into a plate of any required 
gauge, as directed on page 111. 



APPLIED TO DENTISTRY. 



187 



TABLE OF MISCELLANEOUS ALLOYS. 











PARTS 










Name. 


2 

O 

900 
917 


u 

4) 
> 

S3 

900 
925 
901 


u 

a 

a 

D, 
O 

U 

100 
83 

100 
75 
99 

84.5 
90 


a 

H 




a 

a 

N 


03 

O 

2 


6 

a 
■ a 

S 
g 

< 


a 
o 

B 

■4-t 

a 
< 


Gold coins — 
United States. . . 






English 

Silver coins — 
United States. . . 


























English 

Mexico (peso) . . 
Alloys resembling 
gold- 
Dutch gold . . 






























15.5 








Nurnberg gold. 

Green gold 

Red gold 


2.5 
75 

75 


"25 








7.5 














25 

91 
90 

80 

90 

60 

66.6 

1.84 

*88 
.... 














Bronzes — 

For statues. . . . 


2 

10 
20 


1 


6 








Gun metal . , 








Bell metal . . . 












Alumin. bronze. 













10 




German silver. . 






20 
33.3 

*2 


20 




Brass 














Britannia metal 
(English) 






81.90 
"*80 


"io 

20 





*2.*5 


16,25 


Hercules metal. . . 








Pewter 









*Bronze. 



188 CHEMISTR V AND ME TALL URGY 



CHAPTER XVIL 



DENTAL CEnENTS. 

Three varieties of cement are used in dentistry under 
the names of oxyphosphate, oxychloride and oxysulphate 
of zinc. The materials used inpreparing these cements 
consist of a powder which is chiefly zinc oxide and a 
liquid which in the case of the first is a solution of 
glacial phosphoric acid, of the second, a saturated 
solution of zinc chloride and of the last named, a 
dilute solution of zinc chloride or of gum arabic. 
When the powder and the liquid are mixed on 
a glass or on a porcelain plate with a spatula a 
mass is produced which in time owing to some inex- 
plicable change assumes a hard state. The use of 
oxychloride and oxysulphate cements is quite limited 
at the present time. Oxyphosphate, however, is 
extensively employed as a filling material and for 
various other purposes. 

The chief objection to all cements, particularly to 
the oxychloride and oxysulphate, is that they are read- 
ily acted upon by the fluids of the mouth and are there- 
fore of little value as permanent fillings. This ten- 
dency to disintegrate is probably facilitated somewhat 
by the change of volume, usually contraction, which 
they undergo in hardening and by their more or less 



APPLIED TO DENTISTRY. 189 

porous character. For the purpose of counteracting 
the solubility and of conferring greater hardness upon 
the mass when "set" small quantities of such sub- 
stances as silica, ground glass, borax^etc, are added. 
The value, however, of these constituents is question- 
able. Although it is impossible to render cements 
insoluble, it is a noticeable fact that their permanence 
is dependent to a great extent upon the manner of 
preparing, keeping and mixing them. In all cases the 
materials must be properly prepared. It is a fact to 
be observed that the setting and other properties of 
cements are dependent to a high degree upon the 
dehydrated condition of the powder. Hence, in 
working cements care should be taken to protect the 
powder from moisture. Finally, it is observed that to 
give the best results a cement must be thoroughly 
and carefully spatulated into a homogeneous mass. 

Since it is highly essential that the student have 
some understanding of this important class of sub- 
stances, an outline is given below to be followed in 
preparing, testing and otherwise studying them.* 



Oxyphosphate Cement. 

As already stated, oxyphosphate has almost en- 
tirely replaced the other cements for most purposes. 
In this cement the powder usually is specially pre- 
pared zinc oxide. Some manufacturers, however, 
add beside the substances already enumerated small 

*The form of report to be submitted in this work is shown 
in the Appendix, Section II. 



190 CHEMISTR Y AND ME TALL URG Y 

proportions of tin or of bismuth oxide.* It is some- 
times stated that a satisfactory cement powder can 
be made simply by calcining the crude zinc oxide. It 
will be found, however, that the cement will prove more 
satisfactory if the zinc oxide is treated with nitric 
acid previous to calcining. This treatment gives it a 
characteristic " dry fineness/' and renders it some- 
what gritty, no matter how carefully it may have 
been pulverized and sifted. 

In the coloring of oxyphosphate cement, and this 
applies as well to the other varieties, it is seldom nec- 
essary to use any coloring matter. By properly 
manipulating the heat, colors from a light cream to a 
dark yellow can be obtained. To make a light cement 
a heat somewhat above redness may be employed. 
The common dark yellow is best prepared by apply- 
ing a white heat for about two hours. In certain 
cases, however, when special colors are required, 
yellow ocher, lampblack, ferric oxide, etc., may be 
added. 

It is generally recognized that oxyphosphate 
cement is more or less irritating when placed in 
proximity to the pulp. A suggestion of the possible 
cause of this action is found in the fact that cement 
powders contain more or less arsenious oxide. The 
reason for this is that zinc and arsenic are often 
closely associated in nature, and when zinc oxide is 
prepared for a cement powder the treatment often 
fails to remove all the arsenic. Out of fifteen promi- 

*For the composition of several cements as determined by 
analysis, see Appendix, Section II. 



APPLIED TO DENTISTRY. 191 

nent cements analyzed by the author, but two were 
found to contain only traces, while the remainder 
contained from 0.04 to 0.1 per cent of arsenious oxide.* 
Although it is impossible by ordinary methods entirely 
to eliminate arsenic from a cement, the quantity 
is reduced to a mere trace by the treatment already 
described. 

A common complaint with oxyphosphate cement 
is the tendency of the liquid to change with time. 
Thischange sometimes shows itself in the formation of 
small crystals. This can be corrected by carefully 
adding one or more drops of water. In some cases, how- 
ever, the liquid becomes turbid, and finally forms a 
paste-like mass. Of course, in this condition, the 
cement will work imperfectly. The causes of some of 
thechanges which cement liquids undergo as the result 
of " ageing" are not definitely known. It may be 
stated, however, that the purity of the acid employed 
and the care bestowed in preparation are controlling 
factors in these changes. 

Instead of the solution of glacial phosphoric acid, 
the crystals are sometimes used. They are carefully 
melted in a spoon r preferably of platinum, without 
boiling, and after the liquid has cooled somewhat it 
is mixed as usual with the powder. 

PREPARATION OF OXYPHOSPHATE CEMENT. 

Powder. Weigh out in a porcelain dish on the 
laboratory scales about forty-five grams of crude zinc 
oxide. Moisten with concentrated nitric acid, place 

*See table of analyses of cements in the Appendix, Section IL 



192 CHEMISTRY AND METALLURGY 

over a Bunsen burner and apply a gentle heat, con- 
tinually stirring with a glass rod until brown fumes 
cease to come off. Next transfer the powder to a 
clean clay crucible and place it in the furnace. Apply 
a white heat for one or two hours, then remove from 
the furnace, pulverize in a mortar, sift through bolt- 
ing cloth and bottle at once. Take of this fifteen grams 
in a separate bottle, and retain the remainder for use 
later in making the other cements. 

Liquid, For the liquid take ten cubic centimeters 
of distilled water in a test tube and add several pieces 
of glacial phosphoric acid. Allow this to stand, ap- 
plying gentle heat at times and keeping plenty of the 
acid in the tube. When the liquid has reached about 
the consistency of glycerine and is found to mix sat- 
isfactorily with the powder, it may be filtered through 
glass wool to remove any suspended matter and 
then bottled. 

MIXING OXYPHOSPHATE CEMENT. 

In mixing remove the required quantity of liquid 
to the mixing plate by means of a spatula, then pour 
out the powder about an inch from the liquid. Do 
not introduce the spatula into the bottle containing the 
powder. Add small quantities of the powder to the 
liquid, spatulating each portion thoroughly with a 
broad, stiff-bladed spatula until the required consist- 
ency is reached. Since the success of a cement 
depends largely upon the manner in which it is 
mixed, the student should not fail to spatulate thor- 
oughly until a homogeneous mass is obtained. 



APPLIED TO DENTISTRY. 193 

la preparing the samples of cement for the tests 
which follow, the powder should be added until a 
putty-like mass is produced. 

TESTING OXYPHOSPHATE CEMENT. 

/. General Tests. The following tests* have been 
suggested as characterizing a good oxyphosphate 
cement. 

1. When first mixed it should yield a tough mass 
which when removed from the spatula does not 
adhere to the fingers and can be rolled into a pliable 
pellet. 

2. It should have a glassy surface, and at the 
end of two or three minutes it should rebound when 
dropped upon wood, glass or porcelain. 

3. At the end of five minutes it should be quite 
hard and should sound like porcelain when tapped. 

4. After ten or fifteen minutes it should be 
dented with difficulty, and when broken should show 
a clean, sharp fracture. 

5. After twenty minutes it should be very hard 
and should be capable of taking a good burnish. 

6. In thirty minutes it should have little or no 
acid taste. 

Poor cements will often become granular when 
first mixed, and will not so harden but that they can 
be cut like plaster of Paris after an indefinite time. 
Moreover, they will often fail to rebound, and will 
usually have a sticky feeling when pressed between 
the fingers. Finally, they will often retain for hours, 

*See Flagg's ''Plastics and Plastic Filling." 



194 CHEMISTRY AND METALLURGY 

or even for days, an astringent taste. No rule can be 
given for correcting these difficulties. The cement 
powder should be recalcined, and if still unsatis- 
factory the liquid maybe thickened with a little more 
phosphoric acid, or made somewhat thinner by the 
addition of a drop or two of water. It will be neces- 
sary for the student to experiment until the desired 
results are attained. 

2. Tests for Change of Volume. In making these tests 
a sufficient quantity of cement should be mixed to fill 
a cavity in one of the steel blocks (Fig. 29) used in 
testing amalgams. The expansion or contraction 
can then be measured by means of the micrometer 
(Fig, 28). Microscopical examinations of the mar- 
gins should accompany the micrometrical measure- 
ments. 

j. Tests for Strength. Some idea of the strength 
of cements can be gained by preparing blocks as 
described in the corresponding tests under amalgams 
and by crushing these samples in the dynamometer. 
Better results will be obtained if a matrix furnishing 
larger blocks than that described is used. A good 
sized block is 0.125 x 0.125 x 0.125 of an inch. These 
samples, of course, should be given plenty of time to 
harden before they are crushed. 

4. Tests for Porosity. Cements are more or less 
porous, as can be shown by the following tests: Mix 
some cement and roll it into several pellets of equal 
size. Drop these into some red ink or other colored 
liquid in a test tube. Remove the pellets successively 
at intervals of one or two hours, break them open 



APPLIED TO DENTISTRY. 195 

and note how far the coloring matter has penetrated 
them. Some cements will be found to color through- 
out in a short time, while others will require a much 
longer time. 

5. Tests for Arsenic, In testing for arsenic in ce- 
ment powders, the Marsh test (see pages 24 and 114) is 
used. About five grams of the material are dissolved 
in the smallest possible quantity of moderately con- 
centrated hydrochloric acid. When the evolution of 
hydrogen in the apparatus has continued for some 
time and has been tested and found free of arsenic 
by holding a piece of cold porcelain in contact with 
the flame, the solution to be tested is poured in 
through the funnel tube, and a piece of porcelain is 
again held in contact with the flame. If the cement 
in question contains arsenic, a more or less heavy 
deposit of metallic arsenic will be obtained. Since 
arsenic is readily volatilized by heat, the deposit will 
be more marked if the porcelain is not held in one 
position, but is moved about so as to keep a cool sur- 
face against the flame. 

The test just described is used in preference to 
that employed in qualitative analysis, since it is capa- 
ble of detecting smaller quantities. 

After applying the above tests to the cement pre- 
pared as directed, the student should in the same 
manner examine some well-known oxyphosphate 
cements found upon the market. 

Oxychloride Cement. 

Oxychloride cement is used chiefly for lining 
cavities prior to filling them. It is said to exert a 



196 CHEMISTRY AND METALLURGY 

preservative action toward teeth, but is more or less 
irritating. This is commonly attributed to the zinc 
chloride solution. As already stated, it shrinks con- 
siderably, is readily acted upon by the fluids of the 
mouth and hence is valueless as a material for per- 
manent fillings. 

PREPARATION OF OXYCHLORIDE CEMENT. 

Powder, In preparing the powder for this cement 
proceed as follows : Weigh out on the pulp balance 
(Fig. 4) ten grams of the calcined zinc oxide already 
prepared. Thoroughly mix with this one-tenth of a 
gram of borax and two-tenths of a gram of silica. 
Transfer to a clay crucible and calcine in the furnace 
for one-half hour or so at a bright red heat. Remove, 
grind in a mortar, sift through bolting cloth and 
bottle. 

Liquid. To prepare the liquid take 10 c. c. of pure 
concentrated hydrochloric acid and add metallic zinc, 
applying gentle heat occasionally until the acid is 
saturated. Finally, filter through glass wool to 
remove any black specks or pieces of undissolved 
zinc and transfer to a tightly stoppered bottle. 

MIXING OXYCHLORIDE CEMENT. 

The directions given for mixing this cement do 
not differ from those given in mixing oxyphosphate 
cements. A good oxychloride will set in fifteen to 
twenty minutes, but requires several hours in which 
to reach its hardest state. 



APPLIED TO DENTISTRY. 197 

Oxysulphate Cement. 

This cement is usually deficient in hardness but 
as generally stated being nonirritating, it serves a 
useful purpose for protecting pulps and for various 
other purposes. 

PREPARATION OF OXYSULPHATE CEMENT. 

Powder. Take ten grams of the zinc oxide already 
prepared and mix with it four grams of dry zinc sul- 
phate. Transfer to a crucible and calcine in the fur- 
nace as directed in the preparation of oxychloride. 
Pulverize, sift and bottle. 

Liquid. Dissolve two grams of zinc chloride in 
ten cubic centimeters of water. This yields a turbid 
liquid which should be shaken when used. 

MIXING OXYSULPHATE CEMENT. 

The directions given for mixing this cement differ 
but slightly from those just outlined for oxychloride. 
The powder is added to the liquid until a mass not 
thicker than cream is obtained. This cement is ready 
for use when it shows the slightest tendency to 
thicken after being worked for some time with the 
spatula. 



198 CHEMISTR V AND ME TALL URG V 



CHAPTER XVIII. 



SPECIAL PROBLEMS.* 
The Analysis of Teeth. 

Roughly speaking, the solid matter of a tooth is 
composed of thirty per cent of organic and seventy 
per cent of inorganic matter. The organic matter is 
chiefly a substance resembling the ossein in bone. 
Like ossein, it is more or less completely converted 
into gelatine by prolonged boiling with water. The 
inorganic or earthy matter consists mostly of calcium 
phosphate with some magnesium phosphate, calcium 
carbonate and small quantities of other salts. The 
chemical composition of a tooth, however, is not the 
same throughout. Certain parts, namely, the dentine, 
the bulk of the tooth and the cement which covers the 
roots, resembles the bone in composition. On the 
other hand, the enamel which invests the crow T n of 
the tooth contains but little organic matter and is 
composed chiefly of calcium phosphate and fluoride. 

In the table given below the composition of the 
different parts of the tooth is compared. These 
results fail to take into account the water, which con- 
stitutes about five or six per cent of the total weight 
of the tooth. 

*The forms of the reports to be submitted after performing 
the exercises in this chapter are shown in Appendix, Section II. 



APPLIED TO DENTISTRY. 



199 



COMPOSITION OF DENTINE, CEMENT AND ENAMEL COMPARED. 

(VON BIBRA.) 





Dentine. 


Cement. 


Enamel. 


Inorganic matter 

Organic matter 


71.99 
28.01 


70.58 
29.42 


96.41 
3.59 








100.00 


100.00 

60.73 

8.02 
1.00 
0.83 
28.70 
0.72 


100.00 


Calcium phosphate and fluoride. . . 
Calcium carbonate 


66.72 
3.36 
1.18 

0.73 

27.61 

0.40 


89.82 
4.37 


Magnesium phosphate 

Other salts 


1.34 

0.88 


Organic matter 


3.39 


Fat 


0.20 




100.00 


100.00 


100.00 



The inorganic constituents of teeth are insoluble 
in water, but are readily soluble in dilute acids by the 
action of which they may be removed, leaving the 
pliable organic matter which retains the general form 
of the tooth. 

The simple exercises given below will serve to 
show some of the facts just stated. In these tests 
no attempt will be made to show the differences in 
composition between the dentine, the cement and the 
enamel, but the tooth will be considered as a 
whole. 



QUANTITATIVE TESTS. 

i. Estimation of Water. Crush in a mortar a 
freshly extracted tooth which has been freed of adher- 



200 CHEMISTRY AND METALLURGY 

ing matter.* Weigh out one gram on the analytical 
balance in a porcelain crucible, the weight of which 
is known. Place the crucible and its contents in an 
air bath for one hour, at a temperature of 95° C. At 
the end of this time remove the crucible, allow to cool 
and weigh as quickly as possible, in order that the 
hygroscopic residue be prevented from absorbing 
moisture from the air. Return the crucible, after 
weighing, to the bath, and allow it to remain there 
one-half hour. Again cool and weigh. In case the 
weight obtained here corresponds with the previous 
weight the sample may be considered dehydrated. 
When, however, the second heating in the bath 
reduces the weight it will be necessary to again 
heat until a constant weight is obtained. The loss 
in weight, i. e., the difference in weight between the 
original and that obtained after drying, equals the 
weight of water in the sample. This multiplied by 
100 gives the percentage. 

2. Estimation of Organic and I?iorganic Matter. 
Place the crucible containing the dehydrated sample 
on the pipestem triangle. Cover with a crucible cover 
and ignite gently at first until the organic matter is 
burned. Remove the cover and calcine at a red heat 
until the ash is nearly white. Cool and weigh. The 

*In case a freshly extracted tooth cannot be obtained, one 
which has been extracted for some time can be used. Before 
using it for these tests, however, it should be placed in water 
for twenty-four hours or so, in order that the results for water 
may be comparable with those which would be obtained if a fresh 
tooth were used. 



APPLIED TO DEXTISTRY. 201 

loss in weight over that occasioned by the dehydra- 
tion represents the weight of organic matter in the 
sample. This is converted into percentage by multi- 
plying by 100. To obtain the percentage of inorganic 
matter add the percentage values obtained for 
organic matter and water and subtract this result from 
100. 

QUALITATIVE TESTS. 

/. For Orga?iic Matter. Place a tooth in dilute 
hydrochloric acid in a test tube. After two or three 
days the inorganic matter will be removed and the 
soft, elastic organic matter will remain. Boil this 
with water to convert into gelatine, which solidifies 
to a jelly on cooling. 

2. For Phosphates. Transfer the inorganic resi- 
due left from the Quantitative Tests given above to a 
test tube, and dissolve it with heat in dilute hydro- 
chloric acid. Filter out any insoluble specks and 
reserve the filtrate for the tests which are to follow. 
To a few drops of this solution add a drop or two of 
nitric acid, then an excess of ammonium molybdate, 
and boil. Phosphates are indicated by the yellow 
crystalline precipitate of ammonium phospho-molyb- 
date. 

J. For Calcium and Magnesium Phosphates. To 
another portion of the hydrochloric acid solution 
add ammonium hydroxide to alkaline reaction. A 
bulky white precipitate of calcium and magnesium 
phosphates appears. Filter and retain the filtrate for 
the test given below. 



202 CHEMISTR V AND ME TALL URG Y 

4. For Calcium. To the clear filtrate just obtained 
add ammonium oxalate. A white precipitate of cal- 
cium oxalate appears, showing that some calcium is 
present in the tooth uncombined with phosphoric 
acid. This is the calcium present as calcium car- 
bonate, further indicated by the slight effervescence 
when the hydrochloric acid was added to the inor- 
ganic residue. 

ACTION OF VARIOUS SUBSTANCES ON THE TEETH. 

It is evident from facts already observed that the 
inorganic matter of teeth is readily dissolved by acid, 
and it follows then that tooth structure can be greatly 
injured by coming in constant contact with substances 
of an acid character. Among the common mineral acids 
which may exert a disintegrating action upon teeth are 
hydrochloric, nitric, sulphuric and phosphoric, and 
among the vegetable acids are acetic, tartaric, citric, 
lactic, etc. Furthermore many other substances, such 
as ferric chloride (tincture of iron), alum, potassium 
tartrate (cream of tartar), compounds of mercury, 
solutions of hydrogen dioxide, etc., produce injuri- 
ous effects if brought constantly in contact with the 
teeth. 

Analysis of Urine. 

Much research has been made in urine analysis 
with the result that the composition of urine in health 
and" in disease is quite well known. In health it 
always contains certain substances in quite constant 
proportions. Many grave disorders, however, are 



APPLIED TO DENTISTRY. 



203 



accompanied by wide variations in the proportions of 
the normal constituents and by the appearance of 
certain foreign substances. 

In the table given below the average composition 
of urine passed during twenty-four hours is shown. 
Although the acids and metals are separated in this 
table, it must not be inferred that they exist so 
in the urine. They are found in the form of salts : 
Urates, sulphates, phosphates, chlorides, etc. 

The Composition of Normal Urine. 

(Twenty-four hour sample.) 

Water 1500.00 grams. 

Total solids 72.00 »■ 



Urea 33.18 grams. 

Uric acid 0.55 

Hippuric acid 0.40 

Creatinine 0.91 

Pigments and other organic matter.. 10.00 

Sulphuric acid 2.01 

Phosphoric acid 3.16 

Chlorine 7.50 

Ammonia 0.77 

Potassium 2.50 

Sodium 11.09 

Calcium 0.26 

Magnesium 0.21 

It would be impracticable in this course to 
attempt a complete chemical analysis of urine. In- 
deed, such is unnecessary in the analysis of urine for 
clinical purposes. In the following outline only such 
tests and processes will be given as are needed 
to meet the requirements of practical work. For 



204 CHE MIS TR Y AND ME TALL URGY 

more details concerning the significance of certain 
abnormalities the student is referred to books upon 
the subject. 

OUTLINE OF TESTS. 

1. Observation of odor, color, reactions, etc. 

2. Determination of specific gravity. 

3. Tests for albumin. 

4. Test for mucin. 

5. Tests for sugar. 

6. Tests for abnormal coloring matter, 
1. Tests for phosphates and chlorides. 

8. Determination of uric acid. 

9. Determination of urea. 

1. PHYSICAL CHARACTERISTICS. 

Normal urine is of a pale yellow or straw color, 
shading at times to a reddish yellow. If blood is 
present urine may have a reddish brown tint, or 
greenish brown, if bile is present. Fevers, certain 
drugs, and an increase or decrease in the quantity of 
liquids consumed will produce a marked effect upon 
the color of urine. 

At different times during twenty-four hours the 
urine may be alkaline. The whole mixed product, 
however, should be slightly acid in reaction, due, it 
is said, to the presence of acid phosphates, to uric 
acid and to certain other organic acids. In taking 
the reaction, use both the red and the blue litmus 
paper. 

Fresh urine is clear and possesses a peculiar aro- 



APPLIED TO DENTISTRY. 205 

matic odor. Any turbidity is usually due to precipi- 
tated phosphates or urates. If phosphates, they will 
dissolve with a drop of acid; if urates, they will re- 
dissolve with heat. Pus yields a deposit similar 
to that of phosphates. It may be detected under 
the microscope, or by the ropy, gelatinous mass 
formed by the addition of potassium hydroxide to the 
deposit formed after standing. 

2. DETERMINATION OF SPECIFIC GRAVITY. 

The quantity of urine passed by a healthy individ- 
ual in twenty four hours may be taken as about 1500 
c. c. and its specific gravity will range from 1.015 to 
1.025; 1.020 is usually taken as the normal. 

Owing to the fact that in disease the specific 
gravity may run much below or above the normal 
value, its determination is of considerable impor- 
tance in the examination of urine for clinical pur- 
poses. To be of value, however, the specific gravity 
should always be taken upon a sample of the entire 
quantity excreted in twenty-four hours. For a very 
exact determination a special balance known as the 
Mohr-Westphal should be used, although in practical 
work a good urinometer (Fig. 3G) is considered suffi- 
ciently accurate. In using the urinometer pour the 
accompanying cylinder nearly full of urine, allow the 
air bubbles to escape, bring to a proper temperature 
and immerse the urinometer in it. Read the spe- 
cific gravity indicated on the stem below the surface 
of the urine. 

Wide variations in specific gravity nearly always 



206 CHE MIS TR Y AND ME TALL URGY 

occur in certain diseases, particularly in Bright 9 s 
disease and in diabetes mellitus. In the former the 
specific gravity is usually low on the twenty-four hour 
sample, ranging from 1.015 down. On the other 
hand, diabetes mellitus is accompanied by a great 
increase in specific gravity, often reaching 1.040 or 
higher. Quite wide variations in specific gravity are 
often observed in health. These variations result 
from perfectly natural causes. For example, the con- 
sumption of large quantities of liquids will have a 
tendency to decrease the specific gravity, while on the 
other hand excessive perspiration or the consumption 
of small quantities of liquids and large quantities of 
foods will greatly increase the specific gravity, often 
to 1.030, or higher. 

3. TESTS FOR ALBUMIN. 

Albumin is not a constituent of normal urine, 
although it may sometimes be found in the urine of 
healthy individuals. In such cases it is often due to 
slight disorders not difficult to regulate. Albumin 
may appear persistently in the urine, however, in 
quite large quantities as the result of the grave dis- 
order known as Bright's disease. Of the various 
tests proposed for detecting albumin the following 
are usually satisfactory in practical work. Before ap- 
plying the following tests the urine should be filtered if 
cloudy. 

i. Coagulation by Heat. To a test tube nearly 
full of urine add ten or twelve drops of strong nitric 
or acetic acid. Boil the upper part of the tube. A 



APPLIED TO DENTISTRY. 207 

cloud indicates albumin; heat, alone, has the power 
of coagulating albumin, as is shown in the boiling of 
the white of egg. The purpose of the acid here is to 
prevent the precipitation of earthy phosphates which 
usually occurs when urine is boiled. 

2. Coagulation by Nitric Acid % Heat a little strong 
nitric acid in a test tube, and by means of a small 
pipette carefully drop an equal volume of urine on the 
acid so as to perfectly overlie it without mixing. If 
albumin is present a whitish ring of coagulum will 
appear at the junction of the two liquids. The test 
just given may be made with cold nitric acid. In 
this case, however, the acid should be brought under 
the urine by means of the pipette. This test is not 
as reliable as the first, because at times an excess of 
urea in the urine may cause a ring to appear when 
albumin is absent. Heating the acid prevents this. 

4. TEST FOR MUCIN. 

In small quantities mucin has no pathological sig- 
nificance, since it is a constituent of normal urine. 
In catarrh of the urinary tract it may be present in 
considerable quantity, and in such cases it will cause 
a turbidity in the urine when first passed, or soon 
after, and will partly settle and float near the bottom 
of the vessel. Since the turbidity caused by mucin does 
not clear up with acetic or dilute nitric acid, it may 
be mistaken for albumin. They may be distinguished 
as follows: Half fill a test tube with acetic acid, and 
by means of a pipette add the urine so that they do 
not mix. Mucin is indicated by a cloud above the 



208 CHEMISTRY AND METALLURGY 

junction of the two liquids, while albumin appears at 
the junction. 

5. TESTS FOR SUGAR. 

While minute traces of sugar* (dextrose) are said 
to occur in normal urine, relatively large quantities 
indicate the pathological condition known as dia- 
betes mellitus. Urine containing sugar possesses a 
high specific gravity, 1.030 or higher, and the quantity 
is greatly increased. 

While many tests are proposed for detecting sugar, 
the following are reliable if properly carried out. 

i. Fehling's^ Test. Take 5 or 10 c. c. of Fehling's 
solution in a test tube and boil. No precipitation 
should take place. Next add the clear urine drop 
by drop, boiling a moment after each addition. 
If no precipitate forms add a volume of urine equal 
to that of the solution and again boil a moment. If 
sugar is present in even small quantities a yellowish 
precipitate will be formed, which, upon considerable 
boiling, changes to red. (Cu s O.) The above test 
is used quantitatively as well as qualitatively, but in- 
volves more detail than can be given here. For ordi- 
nary purposes, a rough estimation of the quantity of 
sugar present can be made by noting the number of 
drops necessary to bring about a reduction. A pre- 
cipitate occurring after adding but one or two drops 
of urine would indicate a large percentage of sugar. 

*The student must not confuse the sugar found in urine, 
commonly known as dextrose or grape sugar, with common cane 
sugar. The latter does not reduce Fehling's solution. 

fDirections for making and keeping Fehling's solution are 
given in the Appendix, Section I. 



APPLIED TO DENTISTRY. 209 

At times an excessive quantity of uric acid and 
certain other substances may produce an imperfect re- 
duction of the Fehling's solution, shown by the change 
from the blue to a greenish color, or to a nearly color- 
less solution. This, of course, is not to be taken as 
evidence of sugar. In cases where such difficulties 
are encountered the following test may be used: 

2. The Bismuth Test. To some urine in a test 
tube add an equal volume of ten per cent solution of 
potassium hydroxide and then as much pure bismuth 
subnitrate as can be held on the point of a penknife. 
Boil. If sugar is present a black substance consisting 
chiefly of lower oxides of bismuth is formed. If albu- 
min is present in the urine it should be coagulated 
and removed by filtration before applying this test. 

6. TESTS FOR ABNORMAL COLORING MATTER. 

In disease coloring matter, such as bile and blood, 
may appear in the urine. Bile occurs in jaundice and 
gives the urine a dark brown, greenish, or, at times, 
a black color. Blood may appear as the result of 
haemorrhage in any part of the urinary tract, and if 
present in large quantities will impart to the urine a 
deep red color. The following simple tests may be 
employed in detecting the presence of these sub- 
stances: 

/. For Bile Pigments. Pour a small quantity of 
urine into a test tube and introduce below it by means 
of a pipette an equal volume of strong nitric acid 
containing some nitrous acid. If bile is present a 



210 CHEMISTR Y AND METALL URG Y 

series of colors, the most characteristic of which is 
green, will be seen at the junction of the two liquids. 
(Gmelin's test.) 

Another test suggested for detecting bile pigments 
is as follows : Add a few drops of tincture of iodine 
to some urine in the test tube in such a manner that 
the iodine solution floats on the surface. A green 
color at the junction indicates bile (Trousseau's test). 

2. For Blood and Blood Pigments. Examine a 
small quantity of urine by boiling with potassium 
hydroxide. The precipitated earthy phosphates will 
be colored red if the blood is present. 

Another test for blood consists in examining the 
urine under the microscope and detecting the cor- 
puscles which may be present. 

7. TESTS FOR PHOSPHATES AND CHLORIDES. 

Both exist normally in the urine, although in dis- 
ease they may be increased or diminished in quantity. 
To be of value for clinical purposes quantitative tests 
must be made. Here, however, only qualitative tests 
will be given to prove their presence. 

i. For Phosphates. The earthy phosphates usually 
precipitate with heat alone. To remove these add 
ammonium hydroxide and boil. Still another form 
exists in urine, namely, the alkali phosphates. To 
detect them remove the precipitate of earthy phos- 
phates by filtration and add magnesia* mixture. This 
precipitates in the form of ammonium magnesium 

*A solution containing magnesium sulphate, ammonium 
chloride and ammonium hydroxide. 



APPLIED TO DENTISTRY, 211 

phosphate the phosphoric acid which was combined 
with the alkali metals. 

2. For Chlorides. The chlorides in urine exist chiefly 
in the form of sodium chloride or common salt. To 
detect them acidify a small portion of urine with nitric 
acid and add silver nitrate. A white precipitate of 
silver chloride appears. 

8. THE DETERMINATION OF URIC ACID. 

Uric acid occurs normally in the urine in quantities 
varying from 0.4 to 0.8 of a gram daily. It may be 
detected often in the form of reddish crystals in the 
bottom of a vessel in which urine has stood for some 
time. The clinical significance of variations in the 
quantity of uric acid is not very well known. 

To merely detect uric acid add 10 c. c. of strong 
hydrochloric acid to 100 c. c. of urine and allow the 
liquid to stand in a cool place for one or two days. 
Next, filter and wash with water. Transfer to a 
porcelain dish, add a drop of strong nitric acid and 
evaporate to dryness on a water bath. The brown 
residue will turn purple with a drop of ammonium 
hydroxide (Murexid test). 

A rough method for determining uric acid quanti- 
tatively is as follows : Add 25 c. c. of strong hydro- 
chloric acid to 250 c. c. of urine and allow to stand 
as directed above. Collect the sediment on a weighed 
filter and wash with a little cold distilled water. Dry 
and weigh. The result is only approximate. In case 
albumin is present it should be removed before this 
test is made. 



212 CHEMISTR Y AND ME TALL URGY 

9. THE DETERMINATION OF UREA. 

Urea is the most abundant solid constituent in 
urine. In health the average amount excreted is 
thirty-three grams or about two per cent, although 
it may vary widely under different conditions 
since it is dependent upon the quantity and 
quality of food consumed, and upon the losses by 
perspiration, etc. An increase in the quantity of 
urea accompanies diabetes mellitus, fevers, etc., and a 
decrease is seen in diseases of the liver and kidneys. 

To prove merely the presence of urea in urine 
concentrate 50 c. c. to one-quarter its original volume 
and add some strong nitric acid. The urea nitrate 
formed separates as glistening crystals. This test is, 
of course, of no clinical importance, since all urine 
contains urea. 

A method commonly employed for determining 
urea depends upon the fact that a solution of sodium 
hypobromite decomposes this substance into car- 
bonic acid, nitrogen and water. 

CON 2 H 4 +3NaBrO = C0 2 +N 2 +2H 2 0+3NaBr. 

Urea Sodium 

hypobromite 

If now a strongly alkaline solution of sodium 
hypobromite* is used the carbon dioxide is absorbed 
and from the volume of nitrogen set free may be 
calculated the weight of the urea present in the 
volume of urine employed. The apparatus com- 
monly employed is illustrated in Fig. 37. Accom- 

*For the preparation of this solution see Appendix, Section I. 



APPLIED TO DENTISTRY. 213 

panying the illustration is a description of the 
apparatus and the manner of using it. 

Analysis of Saliva.* 

The saliva is secreted by three pairs of salivary 
glands, the parotid, the submaxillary and the sub- 
lingual. The secretions from these glands differ 
somewhat in composition, but are mixed in the 
mouth, and to them are added salivary corpuscles, 
epithelial cells, etc. In the table given below the 
average composition of human saliva is given. It will 
be observed that it consists of about 99.5 per cent 
of water and 0.5 per cent solids. 

The Composition of Mixed Saliva (Jacubowitsch). 

Water 99.51 

Solids 0.48 

Soluble organic bodies, ptyalin, etc 0.1 

Epithelium 0.160 

Inorganic salts 0. 1 v '2 

Potassium sulphocyanate 0.000 

Potassium and sodium chloride 0. 064 

In the following outline of analysis only the 
more important tests and processes'}* will be given, 
and for more facts concerning the significance of 
abnormalities the student should look to some other 

*To collect saliva for this work, wash out the mouth thor- 
oughly with water, then chew a piece of rubber to excite 
secretion. 

f A microscopical study of the sediments in both urine and 
saliva is necessary to render the analysis complete. This sub- 
ject cannot, however, be touched upon in this book. 



214 CHEMISTR Y AND ME TALL URGY 

source. As will be seen, the general method of 
procedure differs but slightly from that outlined for 
the analysis of urine. 

OUTLINE OF TESTS. 

1. Observation of color, odor, consistency, reac- 
tion, etc. 

2. Determination of specific gravity. 

3. Tests for albumin. 

4. Test for mucin. 

5. Test for ptyalin. 

6. Test for sulphocyanates. 

1. Tests for chlorides, phosphates and sulphates. 

8. Tests for calcium and magnesium. 

9. Test for mercury. 

1. PHYSICAL CHARACTERISTICS. 

Normal saliva is colorless, odorless, viscid, frothy 
and slightly turbid. Conditions said to give rise to 
odor in saliva are gingivitis, scurvy, mercurial saliva- 
tion, etc. In reaction saliva is alkaline, due it is said 
to the presence of alkali bicarbonates and phos- 
phates, but the degree of alkalinity varies, being 
greatest during and after meals. Conditions which 
may render the saliva acid in reaction are the decom- 
position of organic matter in the mouth, diabetes 
mellitus, acute rheumatism, mercurial salivation, 
etc. Since it is often difficult to determine the reac- 
tion, especially when nearly neutral, both red and blue 
limus paper should be used. 



APPLIED TO DENTISTRY. 215 

2. DETERMINATION OF SPECIFIC GRAVITY. 

The average amount of saliva secreted in twenty- 
four hours is about 800 or 900 c. c. Obviously it is 
impossible to determine the exact quantity since it 
depends upon so many conditions. The sight or 
even the thought of foods, the mastication of dry 
foods, the filling of teeth, certain drugs and certain 
diseases may greatly increase the quantity of saliva. 
On the other hand, fevers and inflammatory diseases 
decrease the quantity of saliva in a marked degree. 
Specific gravity of normal saliva may range from 
1.002 to 1.009. In taking the specific gravity use the 
urinometer as directed under urine analysis. In case 
the quantity of saliva is insufficient to fill the cylinder, 
measure out a certain quantity of it and dilute it with 
an equal volume of distilled water and multiply the 
last figure of the specific gravity obtained under these 
conditions by 2. The result is the specific gravity of 
the sample. 

3. TESTS FOR ALBUMIN. 

In testing for albumin, which is a normal constitu- 
ent of saliva, apply the tests outlined under urine 
analysis. Before doing so, however, dilute and filter 
the portion to be tested. 

4. TEST FOR MUCIN. 

Mucin is an important constitutent of normal 
saliva and may be detected as outlined under urine 
analysis. 



216 CHEMISTRY AND METALLURGY 

5. TESTS FOR PTYALIN. 

Ptyalin is a diastatic ferment in saliva which has 
the power of converting starch into dextrin and malt- 
ose, the latter being a form of sugar which has the 
power of reducing Fehling's solution. Upon these 
facts is based a method for detecting it. The follow- 
ing tests will serve to prove the presence of ptyalin 
and to show its digestive power : Make a little starch 
paste by mixing one gram of starch in 200 c. c. of cold 
water and then boiling for a few minutes. Cool and 
take a few c. c. in a test tube with an equal volume 
of saliva. Keep warm at a temperature not exceeding 
40° C. for fifteen minutes by passing the test tube 
through the steam from boiling water. At the end 
of this time test the liquid for sugar by means of 
Fehling's solution. The reduction of the Fehling's 
solution is proof of the presence of sugar produced 
by the action of ptyalin in the saliva upon the starch 
solution. 

The activity of this ferment is destroyed by heat, 
by acids and by alkalies. This can be proved by 
repeating the above experiment, having previously 
boiled the saliva or added a drop of strong acid or 
alkali to it. No test for sugar will be obtained in 
these experiments. Another important fact to be noted 
is that saliva has practically no action upon uncooked 
starch. 

6. TEST FOR SULPHOCYANATES. 

Small quantities of alkali sulphocyanates exist in 
the saliva. To detect them proceed as follows: To 



APPLIED TO DENTISTRY. 217 

a small quantity of clear saliva in a test tube add a 
drop of very dilute ferric chloride. A slight reddish 
color, due to the formation of ferric sulphocyanate, 
is formed, which may be removed by the addition of 
mercuric chloride. A comparative test can be made 
by adding an equal quantity of the ferric chloride 
solution to dilute solutions of potassium sulpho- 
cyanate. 

7. TESTS FOR CHLORIDES, PHOSPHATES AND SULPHATES. 

The chlorides in the saliva exist mainly as potas- 
sium and sodium chlorides, while the phosphates and 
sulphates are salts of both alkali and alkaline earth 
metals. 

Before making the tests for these constituents 
evaporate 10 c. c. of saliva to dryness, char the or- 
ganic matter, add a little distilled water and a drop 
or two of acetic acid and filter. Divide the filtrate 
into four parts. 

/. For Chlorides. Test one portion for chlorides 
as directed under urine analysis. 

2. For Phosphates. Test another portion for 
phosphates by adding a drop of nitric acid and an 
excess of ammonium molybdate and boiling. A yel- 
low precipitate, ammonium phospho-molybdate, indi- 
cates phosphates. 

j. For Sulphates. Test a third portion for sul- 
phates by adding a drop of hydrochloric acid and 
some barium chloride, A white precipitate of barium 
sulphate indicates sulphates. 



218 CHEMISTRY AND METALLURGY 

8. TESTS FOR CALCIUM AND MAGNESIUM, 

i. For Calcium. To a fourth portion of the solu- 
tion used in the above tests add ammonium oxalate. 
A white precipitate is calcium oxalate. Filter. 

2. For Magnesium. To the filtrate obtained 
above add ammonium hydroxide to alkaline reaction. 
A white precipitate consists chiefly of ammonium 
magnesium phosphate. 

9. TEST FOR MERCURY. 

Mercury is not a constituent of normal saliva, but 
may be present resulting from the use of drugs con- 
taining mercury. To test for mercury proceed as 
follows: Collect an abundant quantity of saliva and 
make it acid with dilute hydrochloric acid. Digest 
with gentle heat for about two hours, adding 
occasionally a drop of nitric acid or a fragment of 
potassium chlorate. Filter and concentrate the fil- 
trate to one-eighth its original volume. This may 
be tested for mercury by removing a small quantity 
in a test tube, adding a small piece of bright copper 
wire and boiling. The mercury will deposit on the 
copper. 

EFFECTS OF SALIVA UPON METALS. GALVANIC ACTION. 

Galvanic action is often observed in the mouth, 
although it is very slight when the saliva is in a nor- 
mal state. Thus if a nail, a pin or a metallic tooth- 
pick is brought in contact with a filling in a tooth a 
sensation varying from a "metallic " taste in some 
instances to a decided shock in others is experienced. 



APPLIED TO DENTISTRY. 219 

Here the saliva acts as the exciting liquid, and when 
it is strongly acid or alkaline galvanic action may 
result sufficient to bring about the corrosion or even 
the destruction of metals used for various purposes 
in the mouth. This is particularly true if the metals 
coming in contact possess wide electrical differences, 
as aluminum and amalgam or gold. The subject of 
galvanic action in the mouth has not received enough 
study to lead to much definite knowledge con- 
cerning it. 



« • • 



Appendix. 



Tables, Rules, Etc. 



220 APPENDIX. 



APPENDIX. 



SECTION I. 

I. Tables of Weights and Measures. 

In scientific work the French or metric system of 
weights and measures is used almost exclusively. 
Since other systems are in common use, however, 
the relations of these to the metric system are given. 

METRIC MEASURES OF WEIGHT. 

1 milligram = 0.001 gm. = 0.01543 grain. 

10 milligrams = 1 centigram = 0.01 gm. = 0.1543 grain. 
10 centigrams = 1 decigram =0.1 gm. = 1.543 grains. 
10 decigrams = 1 gram = 15.43 grains. 

10 grams = 1 dekagram = 154.324 grains. 

10 dekagrams = 1 hectogram = 100 gms. =3.21 troy ounces. 
10 hectograms = 1 kilogram = 1000 gms. = 32.1 troy ounces. 

The unit of this system is the gram. It is the 
weight of one cubic centimeter of pure water in vacuo 
at 4° C. In scientific work only the milligram, mg., 
the gram, gm., and the kilogram, Kilo., are commonly 
used, and all other denominations are expressed 
in decimals. Thus, if an object weighs two grams 
and five decigrams, the weight would be expressed as 
2.5 grams, etc. 



APPENDIX. 



221 



1 grain 
24 grains 
20 pennyweights 
12 ounces 



TROY WEIGHT. 

1 pennyweight 
1 ounce 
1 pound 



= 0.0648 gram. 
= 1.55 grams. 
= 31.10 grams. 
= 373.2 grams, 



APOTHECARIES WEIGHT. 



1 grain = 

20 grains = 1 scruple = 
3 scruples = 1 drachm = 3.888 
8 drachms = 1 ounce = 31.10 
12 ounces = 1 pound = 373.2 



0.064S gram. 
1.296 grams. 

grams. 

grams. 

grams. 



16 drams 
16 ounces 
25 pounds 

4 quarters 

1 avoirdupois pound 



AVOIRDUPOIS WEIGHT. 

= 1 ounce = 

= 1 pound = 

= 1 quarter = 

1 hundredweight = 



28.35 grams. 
453.59 grams. 
11 .34 kilograms, 
45. 36 kilograms, 
7000 grains. 



METRIC MEASURES OF VOLUME. 

1000 cubic millimeters — 1 cubic centimeter = 0.061 cubic inch. 
1000cubiccentimeters= 1 liter = 61 .027 cubic inches. 

1 cubic centimeter =16.23 minims. 

1 liter = 33.8 fluid ounces. 

28.32 liters = 1 cubic foot. 

The units usually employed in measuring liquids 
in scientific work are the cubic centimeter, c. c, and 
the liter, L. 

FLUID MEASURE. 



1 mimim 
60 minims 



S fluid drachms = 1 fluid ounce 
16 fluid ounces = 1 pint 
8 pints = 1 gallon 

1 gallon 



= 0.0616 cubic centimeter. 
1 fluid drachm = 3.696 cubic centimeters. 
= 29.57 cubic centimeters. 
= 473.179 cubic centimeters. 
= 3.785 liters. 
= 231 cubic inches. 



222 APPENDIX. 

METRIC MEASURES OF LENGTH. 

1 millimeter = 0.03937 inch. 

10 millimeters = 1 centimeter = 0.3937 inch. 
10 centimeters = 1 decimeter = 3.937 inches. 
10 decimeters = 1 meter = 39.37 inches. 

1 inch = 25.4 millimeters. 

1 foot = 0.3048 meter. 

1 yard = 0.9144 meter. 

The units commonly employed in the metric 
measures of length are the millimeter, mm., the 
centimeter, cm. and the meter, M. 

II. Rules for the Conversion of Centigrade 
and Fahrenheit Degrees. 

Two thermometric scales are used, namely, the 
Centigrade and the Fahrenheit. The Centigrade is 
almost exclusively used in scientific work. They 
are mutually convertible by the following rules : 

1. To Convert Centigrade into Fahrenheit; Multiply 
by 9, divide by 5 and add 32. 

2. To Convert Fahrenheit into Centigrade: Subtract 
32, multiply by 5 and divide by 9. 

III. Rules for Determining and for Raising and 
Lowering the Carat of Gold Alloys. 

i. To Determine the Carat of a Given Alloy. Mul- 
tiply 24 by the weight of gold in the alloy and 
divide the product by the total weight of the alloy. 

Example : Determine the carat of the following 
alloy: 



APPEXDIX. 223 

Pure Gold 9 parts. 
Copper 2 M 
Silver 1 M 

12 

The calculation will be 24x9-5-12 = 18. Hence the 
alloy is 18 carats fine. 

In case an alloy of gold has been used in preparing 
the alloy, it will be necessary to first determine the 
quantity of gold present. 

Example : Determine the carat of the following 
alloy : 

Gold (22-carat) 9 parts. 
Copper 2 M 

Silver 1 M 

12 

Since the gold is only 22 carats fine, eleven- 
twelfths of it is gold. Hence the alloy contains 8.25 
parts of pure gold, and the statement will be 24 X 
8.25-*-12=:16.5. Hence the alloy is 16.5 carats fine. 

2. To Raise Gold to a Higher Carat. Multiply the 
weight of the material taken by the difference between 
its carat and that of the metal to be added ; then 
divide this product by the difference between the 
carat of the metal to be added and that of the required 
alloy. The quotient is the total weight of the required 
alloy. Subtract from this the weight of the material 
taken, and the difference is the weight of pure or 
alloyed gold to be added. 

Example: Raise 10 grams of 18-carat gold to 20- 
carat with pure gold. 



224 APPENDIX. 

24—18 = 6 

24—20 = 4 

10X 6h-4 = 15 and 15—10 = 5. Hence 
5 grams of pure gold must be added to the 10 grams 
of 18-carat gold to raise it to 20-carat. 

If, instead of adding pure gold, it is desired to 
use, say 22 carat, then the calculation would be: 

22—18=4 
2f5— 20 = 2 

10X 4-*-2 = 20 and 20 — 10 = 10. Hence 
10 grams of 22-carat gold must be used in this case. 
3. To Reduce Gold to a Required Carat. Multiply the 
weight of material used by its carat and divide this 
product by the required carat. The quotient is the 
weight of the required alloy. From this subtract the 
weight of the material used, and the difference repre- 
sents the weight of inferior metal to be added. 

Example: Reduce 10 grams of pure gold to 18- 
carat. 

10X24-M8 = 13.3 and 13.3—10 = 3.3. Hence 
3.3 grams of inferior metal must be added. 

If the gold to be reduced is not pure, but say 22 
carats fine, then the calculation will be 

10X22^-18 = 12.2 and 12.2—10 = 2.2. Hence 
2.2 grams of inferior metal must be added in this 
case. 

IV. Standard Potassium Cyanide Solution. 

To prepare and standardize a potassium cyanide 
solution for the volumetric estimation of copper pro- 
ceed as follows : Dissolve about 60 grams of potas- 



APPENDIX. 225 

sium cyanide in 1000 c. c. of distilled water. When 
in solution shake thoroughly and transfer to a dry 
glass stoppered bottle, which should be kept in a dark 
place. 

Now weigh out very accurately 0.25 grams pure 
copper foil or wire and place in a small beaker. 
Add about 10 c. c. strong nitric acid and an equal 
quantity of water. Boil until all the copper is in 
solution and the brown fumes have disappeared. 
Transfer to a 100 c. c. flask, washing the beaker several 
times and adding the washings to the flask. Dilute 
to the mark and shake thoroughly. Draw out 50 
c. c. with a pipette (equal to 0.1 25 of a gram of copper), 
transfer to a beaker and add ammonium hydroxide in 
slight excess. When cool, run in the potassium 
cyanide solution from a 50 c. c. burette with constant 
stirring until the blue color is partially destroyed, 
then add about an equal quantity of water and con- 
tinue the addition of potassium cyanide until the blue 
color is destroyed and the color has changed to a faint 
pink. Repeat the operation on the other half of the 
copper solution and take the average of the number 
of cubic centimeters employed. 

Example : If it took 18.2 c. c. potassium cyanide 
solution for 0.125 of a gram of copper (contained in 
50 c. c. of copper solution), then 0.1 25+18.2 =0.00686. 
Hence 1 c. c. of the cyanide solution is equivalent to 
0.00G8G of a gram of copper. 

V. Fehling's Solution. 

Fehling's solution, used in the detection and esti- 
mation of sugar, is a copper sulphate solution contain- 



226 APPENDIX. 

ing an alkali and a tartrate. Since Fehling's solution 
does not keep well it is best to retain the copper sul- 
phate solution and the alkaline tartrate solution in 
separate bottles. When Fehling's solutionis needed 
it can be made by mixing equal volumes of these two 
solutions. 

/. Copper Sulphate Solution, Dissolve 69.28 grams 
of pure crystallized copper sulphate in 500 c. c. of 
distilled water and then dilute to make 1000 c. c. of 
solution. 

2. Alkaline Tartrate Solution, Dissolve 100 
grams of stick sodium hydroxide in 500 c. c. of distilled 
water. When the alkali is dissolved add slowly with 
heat 350 grams of pure Rochelle salt and stir until 
dissolved. Allow the solution to stand for twenty-four 
hours and then filter it through glass wool. Finally, 
add enough water to bring the volume up to 1000 c. c. 

VI. Sodium Hypobromite Solution. 

The sodium hypobromite solution used in deter- 
mining the quantity of urea in urine is prepared as indi- 
cated below. Since it does not keep well, it is best to 
prepare a fresh solution when required. 

Dissolve 100 grams of stick sodium hydroxide in 
250 c. c. of water. When cool, place the vessel con- 
taining this solution in cold water and add slowly 
with constant stirring 25 c. c. of bromine. This 
should be done in a good draft, as the fumes of bromine 
are very irritating. Finally, dilute this solution with 
an equal volume of water before using. 



APPENDIX. 227 

SECTION II. 

I. Forms of Students' Report Sheets. 

It is the custom of the author to require students 
to make reports upon the work done in the laboratory, 
and printed report sheets are furnished for this pur- 
pose. The forms for the various exercises are shown 
below : 

REPORT ON THE ANALYSIS OF UNKNOWN SUBSTANCES. 

Name Section Date 

Solution, metal or alloy 

Metals found. 



Remarks 



REPORT ON THE REFINING OF GOLD, SILVER AND MERCURY. 

Name Section Date 

Weight of scrap gold taken 

Character of scrap 

Method employed. 



Weight of pure gold obtained 

Weight cf scrap silver, or of amalgam, taken, 



Methods employed 



Weight of each metal obtained, 
Remarks : 



228 APPENDIX. 

REPORT ON AMALGAM-ALLOYS AND AMALGAMS. 

Name Section Date 

Formula of amalgam-alloy. . , 

Weight of each metal used 

Weight of ingot obtained 

Loss in melting 

1. Weight in air of each portion of ingot. 

No. 1 . . No. 2 No. 3 

Weight in water of each portion of ingot. 

No. 1 No. 2 No. 3 

Specific gravity of each portion of ingot. 

No. 1 No. 2 No. 3 

Average specific gravity of whole ingot 

Theoretical specific gravity of whole ingot 

How cut — filings or shavings 

Filings. Fine Medium Coarse 

Tests on Freshly Cut Alloy (or Annealed or Oxidized). 

2. Discoloration. Light. ... Medium.. . .Dark .. . 

3. Weight of filings taken 

Weight of mercury taken 

Setting property. Quick. . . Medium. . . Slow. . . 

Character of margins when packed (under 
microscope) 

Character of margins after several days (under 
microscope) 



APPENDIX. 229 

Micrometrical measurements. 

Time Expansion Contraction 



4. Crushing-strength. (Lbs.) 

Flow. . . (Per cent.) Time. . .Pressure. . (Lbs.) 

5. Weight of mercury expressed. 

Percentage composition of amalgam 

Weight of tin removed by mercury 

Percentage of tin in expressed mercury 

Percentage of the total weight of tin in the 

alloy removed 

Remarks : 



Copper Amalgam. 



Remarks 



230 APPENDIX, 

REPORT ON ASSAY OF AMALGAM-ALLOY. 

Name Section Date. . . . 



Percentage composi- Percentage composi- 
tion of alloy as deter- tion of alloy calculated 
mined by assay. from weight of each 

Silver Zinc metal taken in preparing 

Tin Gold. ...... the alloy. 

Copper Total .... Silver Zinc 

Tin Gold 

Copper Total.. . . 

Remarks : 



REPORT ON PREPARATION OF SOLDERS 

Name Section Date , 

Solder or solders prepared 

Quantities prepared , 

Remarks : 



REPORT ON MISCELLANEOUS ALLOYS. 

Name Section Date 

Fusible alloys prepared 

Melting points of alloys as determined by experi- 
ment « 

Remarks: 



APPENDIX. 231 

REPORT ON DENTAL CEMENTS. 

Name Section Date 

Tests on Oxyphosphate Ceme?it. 

1. Results of General Tests. 

1 

2 

3 

4 

5 , 

6 

2. Character of margins when packed (under 
microscope) 

Character of margins after several days (under 

microscope) 

Micrometrical measurements. 
Time Expansion Contraction 



3. Crushing-strength (Lbs.) 

4. Results of Porosity Tests. 



5. Results of Arsenic Test. 


Remarks: 




Oxychloride Cement. 
Remarks: 




Oxysulphate Cement. 
Remarks: 



232 APPENDIX. 

REPORT ON SPECIAL PROBLEMS. 

Name Section Date 

Analysis of Teeth. 
Quantitative tests. 

1. Weight of sample taken 

Weight after dehydration 

Loss due to water 

Percentage of water 

2. Weight of residue after calcining 

Loss due to organic matter 

Percentage of organic matter 

Percentage of inorganic matter 

Qualitative tests. 

1. Results of Tests for Organic Matter 

2. Results of Tests for Phosphates 

3. Results of Tests for Calcium and Magnesiuni 
Phosphates 

4. Results of Test for Calcium 

Remarks: 

Analysis of Urine. 

1. Physical characteristics 

2. Specific gravity 

3. Results of Tests for Albumin 

4. Results of Test for Mucin 

5. Results of Tests for Sugar , 

6. Results of Tests for Abnormal Coloring Matter. 

1. Results of Tests for Phosphates and Chlorides. 



APPENDIX, 233 

8. Weight of uric acid present in 1500 c. c 

9. Weight of urea present in 1500 c. c 

Remarks: 

............ »...»..»...o... ....•••• •••••••••••o« 

Analysis of Saliva. 

1. Physical characteristics 

2. Specific gravity 

3. Results of Tests for Albumin 

4. Results of Test for Mucin » ' 

5. Results of Tests for Ptyalin 

6. Results of Test for Sulphocyanates 

1. Results of Tests for Chlorides, Phosphates and 

Sulphates 

8. Results of Tests for Calcium and Magnesium. 

9, Results of Test for Mercury 

Remarks : 



234 



APPENDIX. 



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INDEX. 



PAGE. 

Acids, action on metals 16 

,( alloys , 95 

Albumin in saliva 215 

in urine 206 

Alloys 16, 88 

change of volume with 

temperature 94 

chemical properties of. 94 

color 92 

conducting power 94 

crystalline form 93 

denned 88 

ductility 93 

elasticity 94 

fusibility 93 

general consideration.. 88 

hardness 94 

liquation of 90 

luster 92 

malleability 93 

miscellaneous 180 

physical properties of . . 91 

preparation of 95 

sonorousness 92 

specific gravity 92 

heat 94 

tenacity 94 

treatment of 77 

Alum, common 34 

Aluminate 34 

Aluminum 33 

alloys of 34 

amalgams 34 

blowpipe tests 35 

bronze 187 

chief ores 34 

compounds 34, 35 

confirmatory reactions. 35 



PAGE. 

Aluminum — Continued. 

in amalgams 34, 139 

metallurgy of 34 

silicates 35 

solubility in acids 34 

steel 34 

Amalgam-alloys 19, 133 

annealing 144 

assay of 155 

composition of some 

well-known 235 

estimation of copper in. 158 

" »' tin " . 156 

11 zinc " . 158 
fire assay for gold and 

silver in 160 

preparing 141 

testing specific gravity of 147 

Amalgamation process. . . .4, 20 

Amalgams.... 16, 21,22,88, 133 

action of saliva on 141 

apparatus for testing. . . 115 
change of form with 

pressure 139 

change of volume 137 

color 135 

copper 31, 153 

crushing strength 139 

defined 88 

discoloration of t . 135 

flow of 140 

" leakage " of 138 

luster 135 

mixing 145 

properties of 135 

solidification 136 

solubility in saliva 141 

special tests for 151 



238 



INDEX. 



PAGE. 

Amalgams — Continued. 

" spheroiding " of 133 

testing. 141, 147 

" for discoloration. . 148 
" " change of vol- 
ume 149 

testing for strength and 

flow , 150 

Ammonia water 52 

Ammonium 52 

blowpipe tests 52 

compounds 52 

confirmatory reaction.. 53 

theory of 52 

Analysis — 

of Group 1 64 

" " II 66 

" III 70 

IV 73 

V 75 

of saliva 213 

of teeth 198 

of urine 202 

qualitative chemical. 60, 155 

quantitative M ... 155 

Analytical balance 97 

Annealing 8, 144 

Antimony 25 

alloys of 26 

blowpipe tests 26 

chief ore 26 

compounds ... . 25 

confirmatory reactions. 26 

effect upon gold 54 

Marsh's test for 26 

metallurgy of 26 

solubility in acids 25 

Apparatus 97 

balances and weights. . . 97 
for testing amalgams. . . 115 
furnaces and accesso- 
ries 103 

measuring 119 

miscellaneous Ill 

urine analysis 121 

Appendix 220 



PAGE. 

Aqua regia 126 

Argentite 20 

Arsenic 23 

acid 24 

alloys of 24 

as an impurity in dental 

cements 190 

as an impurity in zinc 

and tin 24 

chief ore 24 

compounds 23 

confirmatory reactions. . 24 

Marsh's test for 24 

metallurgy of 24 

solubility in acids . . 23 

" " alkalies ... 24 
" fluids of 

the stomach 24 

"white" 23 

Arsenical pyrites 24 

Assay of amalgam-alloys. ... 155 
Autogenous soldering 167 

Babbitt metal. 184 

Balances 97 

analytical 97 

laboratory 1 02 

pulp 102 

Banca tin 27 

Barium 46 

blowpipe test 46 

compounds 46 

confirmatory reactions. 47 

metallurgy of 46 

occurrence 46 

Base metals 2 

Bases 16 

Bauxite 34 

Bell metal 187 

Bessemer process 40 

Bile, Gmelin's test 210 

Trousseau's test 210 

Bismuth 28 

alloys of 29 

as an impurity in mer- 
cury 29 



INDEX. 



239 



PAGE. 

Bismuth — Continued. 

blowpipe test 29 

chief ores 29 

compounds 28 

confirmatory reactions. 29 

effect upon gold 54 

glance 29 

metallurgy 29 

ocher 29 

solubility in acids 28 

subnitrate 28 

Bleaching powder 48 

Block tin 27 

Blood, tests for in urine. .. . 210 

Blower 113 

Blowpipe 113 

Borax 51 

glass 51 

Brass 91, 187 

Britannia metal 187 

Bronzes .... 187 

Bullion mold 110 

Burettes 120 

Button mold 110 

Cadmium 32 

alloys of 32 

blowpipe tests 33 

chief ore. 33 

compounds 32 

confirmatory reactions. . 33 
in amalgam-alloys 32, 135, 136 

metallurgy of 33 

solubility in acids 32 

Calcium 48 

blowpipe test 48 

compounds 48 

confirmatory reactions. . 49 

metallurgy of 48 

occurrence 48 

Calomel 22 

Carat and fineness 55, 222 

Cast iron 40 

Caustic soda 51 

Celestine 47 

Cements \ 188 



PAGE. 

Cements — Continued. 

arsenic in 190 

composition of some 

well-known 234 

general tests 193 

mixing 192, 196; 197 

oxychloride 195 

oxyphosphate 189 

oxysulphate 197 

preparing 191, 196, 197 

tests for arsenic in 195 

11 " change of vol- 
ume 194 

tests for porosity 194 

" strength 194 

Chili saltpeter 51 

Chlorination process 57 

Chlorine water ... 41 

Chrome green 43 

ironstone 43 

steel 43 

yellow 43 

Chromium 42 

alloys of 43 

blowpipe tests 43 

chief ore 43 

compounds 42 

confirmatory reactions. . 43 

metallurgy of 43 

Cinnabar 22 

Clays 36 

Cobalt 45 

alloys of 45 

blowpipe test 46 

chief ores 45 

compounds 45 

confirmatory reactions. . 46 

metallurgy of 46 

Cobaltite 45 

Colored gold 54, 187 

Conductivity for electric- 
ity 13, 94 

for heat 13, 94 

tables of . . . 13 

Conversion of Cen tigrade and 

Fahrenheit degrees.... 222 



240 



INDEX. 



PAGE. 

Copper 30 

alloys of 31 

amalgam 31, 133, 153 

blowpipe tests 31 

chief ores 31 

compounds 30 

confirmatory reactions. . 31 

glance 31 

in amalgam-alloys. .135, 141 

matte 31 

metallurgy of 31 

solubility in acids 30 

Corrosive sublimate 22 

Counterdies, alloy for 185 

Crucibles 108, 

furnace 103 

tongs 109 

Cryolite 34 

Crystallization of metals. ... 6 

of alloys 93 

Cupellation 20, 162 

Cupels 109 

Cupro-manganese 42 

Cyanide process 57 

Cylinders, measuring 119 

Darcet's fusible alloy 182 

Dental amalgams 133 

cements 188 

Dextrin from starch 216 

Dextrose in urine 208 

tests for 208 

Dies, alloys for 183 

properties of 183 

Ductility of alloys 93 

of metals 7 

table of 8 

Dutch gold 187 

Dynamometer 117 

Elasticity of alloys 94 

of metals 9 

Electrical conductivity of al- 
loys 94 

of metals 12 

Elements X 



PAGB. 

Epsom salt 49 

Expansion of alloys 91 

of amalgams 138 

of metals 11 

table of 11 

Extraction of metals from 

ores 3 

Fehling's solution prepara- 
tion 225 

test for sugar 208, 216 

Felspar 35 

Fineness of gold 55, 222 ' 

Flasks, measuring 119 

Flow of amalgams 140 

Fluxes, in soldering 178 

Forms for students* report 

sheets 227 

Fuller's earth 36 

Furnaces 103 

crucible 103 

Hoskins' assay 103 

muffle 105 

other 107 

Fusibility of alloys 93 

of metals 6 

Fusible alloys 29, 93, 180 

determination of melt- 
ing point 182 

preparing 182 

table of 182 

Galena 18 

Galvanic action 15, 141, 218 

Galvanized iron 38 

Gauge plate 112 

German silver 187 

Glauber's salt.. 51 

Gold 53 

alloys of 55 

aluminum solder 171 

beating 54 

blowpipe tests 57 

carat 55 

chief ores 56 



INDEX. 



241 



PAGE. 

Gold — Continued. 

cohesive 55 

coin, composition 187 

colored 54, 187 

compounds , 55 

confirmatory reactions. 57 

determining carat 222 

effects of impurities. ... 54 

fineness 55, 222 

fire assay for 160 

in amalgam-alloys. .135, 136 

metallurgy of 56 

noncohesive 55 

parting 55, 164 

"pickling" 54 

plate 185 

purple of Cassius 57 

raising carat 223 

reducing carat 224 

refining 123 

solders , 175 

solubility in acids 55 

Gravimetric analysis 155 

Green gold 54, 187 

Greenockite 33 

Group 1 64 

II 66 

III 70 

IV 73 

V 75 

reagents 62 

table 63 

Grouping of the metals 62 

Gun metal 187 

Gypsum 48 

Hardness of alloys 94 

of metals 8 

table of 9 

Heavy spar 46 

Hercules metal 187 

Hodgen's fusible alloy 182 

Hydraulic mining 56 

Hydro-carbon blowpipe .... 105 

Hydrogen dioxide 46 

generator 114 



PAGE. 

Ingot mold, upright Ill 

Iron 39 

alloys of 39 

blowpipe tests 41 

cast 40 

chief ores 40 

compounds 39 

confirmatory reactions. . 41 

metallurgy of 40 

pig 40 

solubility in acids 39 

tempering , 41 

wrought 40 

Kaolin or china clay 35 

Laboratory scales 102 

Laughing gas 52 

Lead 17 

alloys of 17 

blowpipe tests 18 

chief ore 18 

compounds 17 

confirmatory reactions. 18 

effect upon gold 54 

metallurgy of 18 

solubility in acid 17 

toughening of 17 

"Leakage" of amalgam fill- 
ings 138 

Lime 48 

slaked 48 

Limestone 48 

Lipowitz's fusible alloy 182 

Liquation of alloys 90 

Litharge 17 

Loam 36 

Lodestone 14 

Luster of alloys 92 

of metals 4 

Magnesia 49 

mixture 210 

Magnesite 49 

Magnesium 49 

blowpipe tests 50 



242 



INDEX. 



PAGE. 

Magnesium — Continued. 

chief ore 49 

compounds 49 

confirmatory reactions. 50 

metallurgy of 49 

solubility in acids 49 

Magnetic quality 14 

Magnetism 14 

Magnets, permanent 14 

Malachite 31 

Malleability of alloys , 93 

of metals 7 

table of 8 

Manganese 41 

alloys of 42 

blowpipe test 42 

brass 42 

bronze 42 

chief ore 42 

compounds 42 

confirmatory reaction... 42 

metallurgy of 42 

Marl . ... 36 

Marsh's apparatus 114 

test for antimony 2G 

M *\ arsenic 24 

Measuring apparatus 119 

Mellotte's fusible alloy 181 

Melting point of alloys 182 

Mercury 21 

alloys of 22 

blowpipe tests 22 

chief ore 22 

compounds 21 

confirmatory reactions. 22 

impurities in 29, 130 

in saliva 218 

refining 130 

solubility in acids 22 

Metallurgy defined 3 

Metals 1 

alloying 95 

base 2 

change of volume 11 

chemical properties of . . 16 

color ...../ 4 



PAGE. 

Metals — Continued. 

conducting power 12 

crystalline form 6 

descriptive details of 

the 17 

diamagnetic 14 

ductility 7 

extraction from ores 3 

fusibility 6 

galvanic action. ....... 14 

general consideration. . 1 

hardness 8 

luster 4 

malleability 7 

noble 2 

occurrence 2 

odor 5 

opacity 4 

paramagnetic 14 

physical properties of . . 4 

specific gravity 5 

" heat 12 

taste ... 5 

tenacity 9 

treatment of 77 

volatility 6 

Metric system 220 

Micrometer, amalgam 115 

Minerals defined ... t 3 

Miscellaneous alloys 180 

apparatus Ill 

Mold, bullion 110 

button... 110 

upright ingot Ill 

"Moldine" 181 

Mosaic gold 27 

Muffle furnace 105 

Newton's fusible alloy 182 

Nickel 44 

alloys of 44 

blende 44 

blowpipe tests 44 

chief ore 44 

compounds 44 

confirmatory reactions . 44 



• INDEX. 



213 



PAGE. 

Nickel — Continued. 

metallurgy of 44 

plating 44 

solubility in acids 44 

Noble metals 2 

Nonmetals 1 

Nurnberg gold 187 

Occurrence of metals 2 

Onion's fusible alloy 182 

Ores 3 

extraction of metals 

from. 3 

Orthoclase 34 

Oxychloride cement 195 

mixing 196 

preparation of 196 

Oxyphosphate cement 189 

mixing 192 

preparation of 191 

testing 193 

Oxysulphate cement 197 

mixing 197 

preparation of 197 

Parting gold 164 

Pattison method 20 

Pearl ash 50 

Pewter 187 

Phosphates in saliva 217 

in teeth 201 

in urine 210 

tests for 201, 210, 217 

Phosphoric acid in cements 188 

Physical properties of alloys 91 

of metals 4 

Pig iron 40 

Pipestem triangles 114 

Pipettes 119 

Placer mining 56 

Plaster of Paris 48 

Platinum , 57 

alloys 59 

aluminum solder 171 

black 58 

blowpipe test. . . 59 



PACE. 

Platinum — Continued. 

chief ore 59 

compounds 58 

confirmatory reactions. . 59 

in amalgam-alloys 136 

metallurgy of 59 

solder 177 

soldering 168 

solubility in acids.. 58 

spongy 58 

Porcelain 36 

crucibles 114 

Potassium 50 

amalgam 50 

blowpipe test 51 

compounds 50 

cyanide solution 224 

dichromate 42 

metallurgy of 50 

occurrence 50 

permanganate 42 

Precipitated copper 31 

Ptyalin in saliva 216 

Puddling process 40 

Pulp balance 102 

Purple of Cassius 57 

Pyrolusite 42 

Qualitative chemical analy- 
sis 60 

Quantitative chemical analy- 
sis 155 

Quartation 56, 128 

Quicksilver 21 

Red fire 47 

gold 187 

lead 17 

precipitate 21 

Refininggold 56 

gold, silver and mercury. 123 

waste dental amalgam. 129 
Report sheets, forms for 

students' 227 

Retort, iron 113 

Richardson's alloys 185 



244 



INDEX. 



PAGE. 

Richmond's fusible alloy. . . 181 

Roiling mill. . Ill 

Rose's fusible alloy 93, 182 

Rules for conversion of Cen- 
tigrade and Fahren- 
heit degrees 222 

for determining carat of 

gold alloys 222 

for soldering 178 

Rust 39 

Sal ammoniac 52 

Saliva, analysis of 213 

composition of 213 

effects of upon metals.. 218 

outline of tests 214 

physical characteristics. 214 

tests for albumin 215 

■■ " calcium 218 

■'■ " chlorides 217 

'• " magnesium... 218 

" mercury 218 

" mucin 215 

11 ptyalin 216 

" reaction 214 

" specific gravity 215 

11 " sulphates 217 

'• " sulphocyanates 216 

Salt common 51 

Saltpeter 50 

Salts 16 

Scheele's green 30 

Scorification 162 

Scorifiers 109 

tongs 109 

Separation of arsenic, anti- 
mony, tin, b i s m u th, 
copper, cadmium, 
mercury and lead. .. . 66 
of barium, strontium 

and calcium 73 

of lead, silver and mer- 
cury 64 

of zinc, aluminum, iron, 
manganese, chronium, 
nickel and cobalt, ... 70 



PAGE. 

Shot, arsenic in 24 

Silex , 36 

Silver 19 

allo)s of 19 

blowpipe tests 21 

chief ores 20 

coin 187 

compounds 19 

confirmatory reactions. . £1 

fire assay for 100 

in amalgam-alloys 

..'19, 133, 135 

metallurgy of 20 

refining 20, 129 

solders 173 

solubility in acids 19 

"spitting" 19 

" Silvering " mirrors 27 

Smalt 45 

Smaltite 45 

Soda. 51 

Sodium 51 

amalgam 51 

blowpipe test 51 

compounds 51 

hypobromite solution . . 226 

metallurgy of 51 

occurrence 51 

Soft solders 169 

Soldering, rules for 178 

Solders 167 

bismuth. 170 

brass 173 

chemical 170 

classification 168 

for aluminum 170 

bronze ... 177 

for platinum 177 

gold 173 

hard 173 

preparation of 168 

silver 173 

soft 169 

tin 169 

Solutions, Fehling's 225 

potassium cyanide 224 



INDEX. 



245 



PAGE. 

Solutions — Continued. 

sodium hypobromite . . . 226 

Special problems 198 

Specific gravity of alloys. 92, 147 

of metals 5 

of saliva 215 

of urine 205 

Specific heat of alloys 94 

of metals 12 

Spelter solder 176 

Spence's " metal " 184 

' Spheroiding" of amalgams. 138 

Spongy platinum 58 

Standard solution 155 

potassium cyanide 224 

Stannite 80 

Steel 40 

Stibnite 26 

Strontianite 47 

Strontium 47 

blowpipe test 47 

compounds 47 

confirmatory reactions.. 47 

metallurgy of 47 

occurrence 41 

Sugar tests 208 

Sulphocyanates in saliva... 216 

Sweepings, refining 124 

Sympathetic ink 45 

Table, analyses of amalgam- 
alloys 235 

cements 234 

group 63 

I 80 

II 81, 82 

III 83 

IV 84 

V 85 

VI 86, 87 

of conductivity 13 

of ductility 8 

of expansion of metals. . 11 

of hardness 9 

of malleability 8 

of miscellaneous alloys. 187 



PAGE. 

Table — Continued. 

of specific heats 13 

of tenacity 10 

of weights and measures 220 
Teeth, action of substances on 202 

analysis of 198 

composition of 199 

estimation of inorganic 

matter in 200 

estimation of organic 

matter in 200 

estimation of water in. . 199 

ossein in 198 

qualitative analysis of. . 201 
quantitative " " . . 199 
tests for calcium in.... 202 
11 " calcium phos- 
phate in 201 

test for ossein in 201 

•■ " phosphates in.. 201 

Tempering 41 

Testing for magnesium, po- 
tassium, sodium and 

ammonium 75 

Theory of ammonium 52 

Thermo-electricity 15 

Thermometers, Centigrade 

and Fahrenheit 222 

Tin 27 

alloys of 27 

amalgam 27, 136 

Banca 27 

block 27 

blowpipe test 27 

chief ore 27 

compounds 27 

confirmatory reactions. 28 

in amalgam-alloys 136 

metallurgy of 27 

solubility in acids. 27 

Tin stone 27 

Tongs, crucible 108 

cupel 109 

scorifier 109 

Treatment of metals and 

alloys 77 



246 



INDEX. 



PAGE. 

Type metal 184 

Ultramarine 36 

Urea in urine 212 

Ureometer, Doremus' 121 

Uric acid in urine 211 

Urine analysis. . . . . . ... 202 

analysis apparatus 121 

composition of 203 

outline of tests , . 204 

physical characteristics. 204 

tests for albumin 206 

" " chlorides 210 

" M coloring matter 209 

" '■ mucin 207 

" M phosphates.... 210 
" " specific gravity 205 

•' " sugar 208 

n " urea 212 

" " uric acid 211 

Urinometer 121 

Vein mining 56 

Vermilion ..... 22 

Volumetric analysis 155 

determination of copper 
in amalgam-alloys... 158 



PAGE. 

Weights 99 

tables of 220 

" White" arsenic 23 

lead 17 

Wood's fusible alloy 182 

Wrought iron 40 

Yellow ocher 36 

Zinc 87 

alloys of 38 

blende 38 

blowpipe tests 38 

chief ore 38 

compounds 37 

confirmatory reactions. 38 

contraction of 183 

dies 37, 183 

in amalgam-alloys. .135, 138 

in gold solders 175 

metallurgy of 38 

oxychloride 188 

oxyphosphate 188 

oxysulphate 188 

purification 37 

solubility in acids 38 

Zincate 38 



Our name or tracks (TTT mark > wbereuer 
seen, is a guaran= r*2\ tee of excellence 

The Great Forward A 
Movement in W 

Dentistry 

grows apace 

This is apparent alike in the requirements as to the qualifica- 
tions and work of the students entering our colleges, the gradu- 
ates leaving them, the professional instructors and private prac- 
titioners. ALL feel the mighty impulse derived from strengthened 
vision and the high altitudes from which tbrey view the masterly 
possibilities of the dental profession in this dawn of the second 
century of our national life. 

We believe it may be truthfully said that we, as manufac- 
turers and dealers, have kept abreast of and much of the time 
anticipated the demands of the profession, in furnishing high 
grade tools and materials. 

New evidence of alertness appeared recently when that scien- 
tific investigator and indefatigable worker, Dr. G. V. Black, M. 
D., D. D.S., Sc. D., Dean of the Dental Department of the North- 
western University, so well known and greatly respected wher- 
ever dentistry is practiced, conceived and successfully conducted 
a course in M Amalgam Making " in Chicago. 

Our chemist and metallurgist was promptly on hand, took 
the course, received his certificate, and we will, a little later, place 
upon the market an amalgam made in comformity with Dr. 
Black's ideas and meeting fully his requirements. 

You will find at our Chicago house a complete stock of 
up-to-date dental supplies. Our representatives will be found to 
be experienced and courteous, with exceptional facilities for sup- 
plying your needs from the least to the largest item of dental 
requirements. 

We serve you courteously, conscientiously, carefully and 
promptly. Try us. 

GIDEON SIBLEY 

N. W. Cor. State and Quincy Sts. 
PHILADELPHIA, PA. Chicago, 111. 



CHEMICAL APPARATUS 



AND CHEMICALS OF 
EVERY DESCRIPTION 



Furnaces, 



Tongs, Mf 

Bellows, v *?* 

Blowpipes, 
Molds, 
*j|n Charcoals, 

&* Metals, 

Etc., etc. 

Bacteriological Apparatus 

Culture Ovens, 
Thermostats, 
Sterilizers, 
Etc. 



REICHERT'S CELEBRATED MICROSCOPES 
AND ACCESSORIES 



Ricftaras § Co* 

Limited 

CHICAGO : NEW YORK : 

108 Lake Street. 30 E. Eighteenth St 



Benefit 



GET W"^ /% • i OF HIGH-GRADE GOODS AT LOW 

THE Lf /\^« /\4-^4- PRICES BY DEALING WITH 

US DIRECT. 



As we are large refiners of precious metals, and as we make a specialty of 
manufacturing gold plate and gold solders for the dental trade, we are in a 
position to make you lower prices than it is possible for you to get elsewhere. 
You do not run any risk in purchasing of us, for the reason that all our goods 
are put up with conscientious, painstaking care, backed by experience, skill 
and determination to turn out only the very best material, which gives our 
goods their satisfactory quality. The lack of any of these marks the difference 
between success and failure. You can always depend on getting what you 
want. You pay what is fair — you are satisfied. Study our price list below. 

PRICE LIST. 

Per Dwt. 

Clasp Metal $ .85 

Clasp Wire 1.00 

18K Gold Wire 95 

20K " 1.05 

24K " 1.20 

Platinum Sheet or Wire 

market price 

Platinum Irido Sheet or Wire 

market price 

Perfection Alloy, per oz $2.00 

11 " three ozs 5.00 

Aluir.inum, per oz 10 

All metals cut 
to pattern without extra charge. 

Granulated Silver, pure, for making dental alloy market price 

" Tin, " " " " market price 

11 Copper, '' " " '• market price 

" Zinc, M " " '• market price 

Antimony, " " M " market price 

Bismuth, " " " " market price 

WE PAY THE FOLLOWING CASH PRICES FOR 

Scrap Gold, Platinum, Etc. 

Per Dwt. Per Dwt. 

Gold Fillings $1.00 Gold Filings $ .60 to $ .75 

Gold Scrap $ .72 to .88 Platinum market price 

BENCH AND FLOOR SWEEPINGS REFINED. 

MAIL ORDERS GIVEN PROMPT ATTENTION. 



14K Solder 


Per Dwt. 
$ .75 


16K " 


80 


18K " 


85 


20K " 


95 


22K " 


1.05 


Coin Solder 


1.00 


Silver Solder, per oz.. . 


1.00 


18K Gold Plate 

20K " 


85 

95 


22K " 


. 1.05 


24K «' 

Coin Gold 


1.10 

1.05 



Thomas J. Dee & Co. 

GOLD AND SILVER REFINERS, ASSAYERS AND SWEEP SMELTERS , 

67 and 69 Washington Street, 
CHICAGO. 



NO DUST 

NO ASHES 

CHEAP 

EFFECTIVE 

ECONOMICAL 

PORTABLE 

AND 

AUTOMATIC 



Hoskins' Patent 
Hydro-Carbon 
Blowpipe and 
Assay Furnaces 



SS&. 



SEND FOR PRICE 
LIST TO 



WUHQFTMC « South Clark St., Room 51 
♦ nUOraiNO CHICAGO, ILLINOIS 




THE 



Clark Fountain Spittoon 

has revolving inner bowl, one supply jet, 
valves without packing, no gurgling, no 
splashing, nothing in the center to obstruct 
waste, is noiseless, beautiful, and simple. 



The Clark Dental Engine 

fitted with the Harris pneumatic head and 
mallet or with single head, has swinging 
standard. Easy running, finest finish. 



WE BACK THESE GOODS 
WITH OUR REPUTATION 



6PECIAL PRICES TO STUDENTS 

ADDRESS A. C. CLARK & CO., GENERAL AGENTS 
HARVARD COMPANY DENTAL 
AND SURGICAL CHAIRS 
908-909 MASONIC TEMPLE CHICAGO, ILLINOIS 




$& S3SS 




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